boinc/vda/ssim.cpp

977 lines
26 KiB
C++

// This file is part of BOINC.
// http://boinc.berkeley.edu
// Copyright (C) 2011 University of California
//
// BOINC is free software; you can redistribute it and/or modify it
// under the terms of the GNU Lesser General Public License
// as published by the Free Software Foundation,
// either version 3 of the License, or (at your option) any later version.
//
// BOINC is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
// See the GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with BOINC. If not, see <http://www.gnu.org/licenses/>.
// ssim - simulator for distributed storage
//
// Simulates the storage of files on a dynamic set of hosts.
// usage: ssim
// [--policy filename]
// [--host_life_mean x]
// [--connect_interval x]
// [--mean_xfer_rate x]
// [--file_size x]
//
// outputs:
// stdout: log info
// summary.txt: format
// fault tolerance min
// disk_usage mean
// upload_mean
// download_mean
#include <math.h>
#include <limits.h>
#include <stdio.h>
#include <string.h>
#include <set>
#include "des.h"
#include "vda_lib.h"
using std::set;
// We simulate policies based on coding and replication.
//
// Coding means that data is divided into M = N+K units,
// of which any N are sufficient to reconstruct the original data.
// When we need to reconstruct an encoded unit on the server,
// we try to upload N_UPLOAD subunits,
// where N <= N_UPLOAD <= M
// The units in an encoding can themselves be encoded.
//
// The bottom-level data units ("chunks") are stored on hosts,
// possibly with replication
struct PARAMS {
// The model of the host population is:
// - the population is unbounded
// - host lifetime is exponentially distributed
// - the time needed to transfer n bytes of data to/from a host is
// U1*connect_interval + (U2+.5)*n/mean_xfer_rate;
// where U1 and U2 are uniform random vars
// (U1 is per-transfer, U2 is per-host)
//
double host_life_mean;
double connect_interval;
double mean_xfer_rate;
double file_size;
double sim_duration;
PARAMS() {
// default parameters
//
host_life_mean = 100.*86400;
connect_interval = 86400.;
mean_xfer_rate = .2e6;
file_size = 1e12;
sim_duration = 1000.*86400;
}
} params;
POLICY policy;
// Terminology:
//
// A data unit is "recoverable" if it can be recovered on the server
// by uploading data from hosts.
// A chunk is recoverable if it's present on the server or on at least 1 host.
// (note: if it's downloading, it's still present on the server)
// An encoded data unit is recoverable if at least N
// of its subunits are recoverable.
// Figures of merit
//
// for each file, we compute:
// - the average and peak server network rate, up and down
// - the average and peak disk usage
// - the average and min fault tolerance level
// (i.e. number of simultaneous host failures needed to lose the file)
//
// These are measured starting from the time when the file's
// initial downloads have all succeeded or failed
#define EVENT_DEBUG
#define SAMPLE_DEBUG
//#define RECOVERY_DEBUG
SIMULATOR sim;
int next_file_id=0;
int next_host_id=0;
inline double drand() {
return (double)rand()/(double)RAND_MAX;
}
double ran_exp(double mean) {
return -log(drand())*mean;
}
char* time_str(double t) {
static char buf[256];
struct tm;
int n = (int)t;
int nsec = n % 60;
n /= 60;
int nmin = n % 60;
n /= 60;
int nhour = n % 24;
n /= 24;
sprintf(buf, "%4d days %02d:%02d:%02d", n, nhour, nmin, nsec);
return buf;
}
char* now_str() {
return time_str(sim.now);
}
struct CHUNK;
struct CHUNK_ON_HOST;
struct META_CHUNK;
struct DFILE;
struct HOST;
set<HOST*> hosts;
// Represents a host.
// The associated EVENT is the disappearance of the host
//
struct HOST : public EVENT {
int id;
double transfer_rate;
set<CHUNK_ON_HOST*> chunks; // chunks present or downloading
virtual void handle();
HOST() {
t = sim.now + ran_exp(params.host_life_mean);
id = next_host_id++;
transfer_rate = params.mean_xfer_rate*(drand() + .5);
hosts.insert(this);
}
};
#if 0
// The host arrival process.
// The associated EVENT is the arrival of a host
//
struct HOST_ARRIVAL : public EVENT {
virtual void handle() {
sim.insert(new HOST);
t += ran_exp(86400./HOSTS_PER_DAY);
sim.insert(this);
}
};
#endif
void die(const char* msg) {
printf("%s: %s\n", now_str(), msg);
exit(1);
}
// The status of a chunk on a particular host.
// The associated event is the completion of an upload or download
//
struct CHUNK_ON_HOST : public EVENT {
HOST* host;
CHUNK* chunk;
char name[256];
bool present_on_host;
bool transfer_wait; // waiting to start transfer
bool transfer_in_progress; // upload if present_on_host, else download
virtual void handle();
void start_upload();
void start_download();
inline bool download_in_progress() {
return (transfer_in_progress && !present_on_host);
}
void remove();
};
#define PRESENT 0
#define RECOVERABLE 1
#define UNRECOVERABLE 2
// base class for chunks and meta-chunks
//
struct DATA_UNIT {
virtual void recovery_plan(){};
virtual void recovery_action(){};
int status;
bool in_recovery_set;
bool data_now_present;
bool data_needed;
double cost;
int min_failures;
// min # of host failures that would make this unrecoverable
char name[64];
};
struct CHUNK : DATA_UNIT {
set<CHUNK_ON_HOST*> hosts;
META_CHUNK* parent;
double size;
bool present_on_server;
CHUNK(META_CHUNK* mc, double s, int index);
void start_upload();
void host_failed(CHUNK_ON_HOST* p);
bool download_in_progress();
void upload_complete();
void download_complete();
void assign();
virtual void recovery_plan();
virtual void recovery_action();
};
struct META_CHUNK : DATA_UNIT {
vector<DATA_UNIT*> children;
META_CHUNK* parent;
int n_children_present;
bool have_unrecoverable_children;
DFILE* dfile;
bool uploading;
CODING coding;
META_CHUNK(
DFILE* d, META_CHUNK* par, double size, int coding_level, int index
);
virtual void recovery_plan();
virtual void recovery_action();
};
// keeps track of a time-varying property of a file
// (server disk usage, up/download rate, fault tolerance level)
//
typedef enum {DISK, NETWORK, FAULT_TOLERANCE} STATS_KIND;
struct STATS_ITEM {
STATS_KIND kind;
double value;
double integral;
double extreme_val;
double extreme_val_time;
double prev_t;
double start_time;
bool first;
char name[256];
FILE* f;
void init(const char* n, const char* filename, STATS_KIND k) {
f = fopen(filename, "w");
strcpy(name, n);
kind = k;
value = 0;
integral = 0;
switch (kind) {
case DISK:
case NETWORK:
extreme_val = 0;
break;
case FAULT_TOLERANCE:
extreme_val = INT_MAX;
break;
}
extreme_val_time = 0;
first = true;
}
void sample(double v, bool collecting_stats) {
#ifdef SAMPLE_DEBUG
switch (kind) {
case DISK:
printf("%s: %s: %fGB -> %fGB\n", now_str(), name, value/1e9, v/1e9);
break;
case NETWORK:
printf("%s: %s: %fMbps -> %fMbps\n", now_str(), name, value/1e6, v/1e6);
break;
case FAULT_TOLERANCE:
printf("%s: %s: %.0f -> %.0f\n", now_str(), name, value, v);
break;
}
#endif
double old_val = value;
value = v;
if (!collecting_stats) return;
if (first) {
first = false;
prev_t = sim.now;
return;
}
double dt = sim.now - prev_t;
prev_t = sim.now;
integral += dt*old_val;
switch (kind) {
case DISK:
case NETWORK:
if (v > extreme_val) {
extreme_val = v;
extreme_val_time = sim.now;
}
break;
case FAULT_TOLERANCE:
if (v < extreme_val) {
extreme_val = v;
extreme_val_time = sim.now;
}
break;
}
fprintf(f, "%f %f\n", sim.now, old_val);
fprintf(f, "%f %f\n", sim.now, v);
}
void sample_inc(double inc, bool collecting_stats) {
sample(value+inc, collecting_stats);
}
void print() {
sample_inc(0, true);
double dt = sim.now - start_time;
switch (kind) {
case DISK:
printf(" mean: %fGB. Max: %fGB at %s\n",
(integral/dt)/1e9, extreme_val/1e9, time_str(extreme_val_time)
);
break;
case NETWORK:
printf(" mean: %fMbps. Max: %fMbps at %s\n",
(integral/dt)/1e6, extreme_val/1e6, time_str(extreme_val_time)
);
break;
case FAULT_TOLERANCE:
printf(" mean: %.2f. Min: %.0f at %s\n",
integral/dt, extreme_val, time_str(extreme_val_time)
);
break;
}
}
void print_summary(FILE* f) {
double dt = sim.now - start_time;
switch (kind) {
case DISK:
fprintf(f, "%f\n", integral/dt);
break;
case NETWORK:
fprintf(f, "%f\n", integral/dt);
break;
case FAULT_TOLERANCE:
fprintf(f, "%f\n", extreme_val);
break;
}
}
};
// represents a file to be stored.
// The associated EVENT is the arrival of the file
//
struct DFILE : EVENT {
META_CHUNK* meta_chunk;
double size;
int id;
#if 0
set<HOST*> unused_hosts;
// hosts that don't have any chunks of this file
#endif
int pending_init_downloads;
// # of initial downloads pending.
// When this is zero, we start collecting stats for the file
double accounting_start_time;
STATS_ITEM disk_usage;
STATS_ITEM upload_rate;
STATS_ITEM download_rate;
STATS_ITEM fault_tolerance;
DFILE(double s) {
id = next_file_id++;
#if 0
unused_hosts = hosts;
#endif
size = s;
disk_usage.init("Disk usage", "disk.dat", DISK);
upload_rate.init("Upload rate", "upload.dat", NETWORK);
download_rate.init("Download rate", "download.dat", NETWORK);
fault_tolerance.init("Fault tolerance", "fault_tol.dat", FAULT_TOLERANCE);
}
// the creation of a file
//
virtual void handle() {
meta_chunk = new META_CHUNK(this, NULL, size, 0, id);
#ifdef EVENT_DEBUG
printf("created file %d: size %f encoded size %f\n",
id, size, disk_usage.value
);
#endif
meta_chunk->recovery_plan();
meta_chunk->recovery_action();
}
inline bool collecting_stats() {
return (pending_init_downloads == 0);
}
void recover() {
meta_chunk->recovery_plan();
meta_chunk->recovery_action();
fault_tolerance.sample(meta_chunk->min_failures-1, collecting_stats());
}
void print_stats() {
printf("Statistics for file %d\n", id);
printf(" Server disk usage:\n");
disk_usage.print();
printf(" Upload rate:\n");
upload_rate.print();
printf(" Download rate:\n");
download_rate.print();
printf(" Fault tolerance level:\n");
fault_tolerance.print();
FILE* f = fopen("summary.txt", "w");
fault_tolerance.print_summary(f);
disk_usage.print_summary(f);
upload_rate.print_summary(f);
download_rate.print_summary(f);
fclose(f);
}
};
//////////////////// method defs ////////////////////
void CHUNK_ON_HOST::start_upload() {
transfer_in_progress = true;
transfer_wait = true;
t = sim.now + drand()*params.connect_interval;
#ifdef EVENT_DEBUG
printf("%s: waiting to start upload of %s\n", now_str(), name);
#endif
sim.insert(this);
}
void CHUNK_ON_HOST::start_download() {
transfer_in_progress = true;
transfer_wait = true;
t = sim.now + drand()*params.connect_interval;
#ifdef EVENT_DEBUG
printf("%s: waiting to start download of %s\n", now_str(), name);
#endif
sim.insert(this);
}
// transfer or transfer wait has finished
//
void CHUNK_ON_HOST::handle() {
if (transfer_wait) {
transfer_wait = false;
if (present_on_host) {
#ifdef EVENT_DEBUG
printf("%s: starting upload of %s\n", now_str(), name);
#endif
chunk->parent->dfile->upload_rate.sample_inc(
host->transfer_rate,
chunk->parent->dfile->collecting_stats()
);
} else {
#ifdef EVENT_DEBUG
printf("%s: starting download of %s\n", now_str(), name);
#endif
chunk->parent->dfile->download_rate.sample_inc(
host->transfer_rate,
chunk->parent->dfile->collecting_stats()
);
}
t = sim.now + chunk->size/host->transfer_rate;
sim.insert(this);
return;
}
transfer_in_progress = false;
if (present_on_host) {
// it was an upload
#ifdef EVENT_DEBUG
printf("%s: upload of %s completed\n", now_str(), name);
#endif
chunk->parent->dfile->upload_rate.sample_inc(
-host->transfer_rate,
chunk->parent->dfile->collecting_stats()
);
chunk->upload_complete();
} else {
present_on_host = true;
#ifdef EVENT_DEBUG
printf("%s: download of %s completed\n", now_str(), name);
#endif
chunk->parent->dfile->download_rate.sample_inc(
-host->transfer_rate,
chunk->parent->dfile->collecting_stats()
);
chunk->download_complete();
}
}
void CHUNK_ON_HOST::remove() {
if (transfer_in_progress) {
sim.remove(this);
if (!transfer_wait) {
if (present_on_host) {
chunk->parent->dfile->upload_rate.sample_inc(
-host->transfer_rate,
chunk->parent->dfile->collecting_stats()
);
} else {
chunk->parent->dfile->download_rate.sample_inc(
-host->transfer_rate,
chunk->parent->dfile->collecting_stats()
);
}
}
}
}
// the host has failed
//
void HOST::handle() {
set<HOST*>::iterator i = hosts.find(this);
hosts.erase(i);
#ifdef EVENT_DEBUG
printf("%s: host %d failed\n", now_str(), id);
#endif
set<CHUNK_ON_HOST*>::iterator p;
for (p = chunks.begin(); p != chunks.end(); p++) {
CHUNK_ON_HOST* c = *p;
c->chunk->host_failed(c);
c->remove();
delete c;
}
}
CHUNK::CHUNK(META_CHUNK* mc, double s, int index) {
parent = mc;
present_on_server = true;
size = s;
sprintf(name, "%s.%d", parent->name, index);
parent->dfile->pending_init_downloads += policy.replication;
parent->dfile->disk_usage.sample_inc(size, false);
}
// if there aren't enough replicas of this chunk,
// pick new hosts and start downloads
//
void CHUNK::assign() {
if (!present_on_server) return;
while ((int)(hosts.size()) < policy.replication) {
#if 0
if (parent->dfile->unused_hosts.size() == 0) {
die("no more hosts!\n");
}
set<HOST*>::iterator i = parent->dfile->unused_hosts.begin();
HOST* h = *i;
parent->dfile->unused_hosts.erase(i);
#else
HOST* h = new HOST;
sim.insert(h);
#endif
CHUNK_ON_HOST *c = new CHUNK_ON_HOST();
sprintf(c->name, "chunk %s on host %d", name, h->id);
#ifdef EVENT_DEBUG
printf("%s: assigning chunk %s to host %d\n", now_str(), name, h->id);
#endif
c->host = h;
c->chunk = this;
h->chunks.insert(c);
hosts.insert(c);
c->start_download();
}
}
bool CHUNK::download_in_progress() {
set<CHUNK_ON_HOST*>::iterator i;
for (i=hosts.begin(); i!=hosts.end(); i++) {
CHUNK_ON_HOST* c = *i;
if (c->download_in_progress()) return true;
}
return false;
}
void CHUNK::start_upload() {
// if no upload of this chunk is in progress, start one.
// NOTE: all instances are inherently present_on_host,
// since this is only called if chunk is not present on server
//
CHUNK_ON_HOST* c;
set<CHUNK_ON_HOST*>::iterator i;
for (i=hosts.begin(); i!=hosts.end(); i++) {
c = *i;
if (c->transfer_in_progress) return;
}
c = *(hosts.begin());
c->start_upload();
}
void CHUNK::host_failed(CHUNK_ON_HOST* p) {
set<CHUNK_ON_HOST*>::iterator i = hosts.find(p);
hosts.erase(i);
#ifdef EVENT_DEBUG
printf("%s: handling loss of %s\n", now_str(), p->name);
#endif
parent->dfile->recover();
}
void CHUNK::upload_complete() {
if (!present_on_server) {
present_on_server = true;
parent->dfile->disk_usage.sample_inc(
size,
parent->dfile->collecting_stats()
);
}
parent->dfile->recover();
}
void CHUNK::download_complete() {
if (parent->dfile->pending_init_downloads) {
parent->dfile->pending_init_downloads--;
}
parent->dfile->recover();
}
META_CHUNK::META_CHUNK(
DFILE* d, META_CHUNK* par, double size, int coding_level, int index
) {
dfile = d;
parent = par;
coding = policy.codings[coding_level];
if (parent) {
sprintf(name, "%s.%d", parent->name, index);
} else {
sprintf(name, "%d", index);
}
if (coding_level<policy.coding_levels-1) {
for (int j=0; j<coding.m; j++) {
children.push_back(new META_CHUNK(
d,
this,
size/coding.n,
coding_level+1,
j
));
}
} else {
for (int j=0; j<coding.m; j++) {
children.push_back(
new CHUNK(this, size/coding.n, j)
);
}
}
}
// sort by increasing cost
//
bool compare_cost(const DATA_UNIT* d1, const DATA_UNIT* d2) {
return d1->cost < d2->cost;
}
// sort by increase min_failures
//
bool compare_min_failures(const DATA_UNIT* d1, const DATA_UNIT* d2) {
return d1->min_failures < d2->min_failures;
}
// Recovery logic: decide what to do in response to
// host failures and upload/download completions.
//
// One way to do this would be to store a bunch of state info
// with each node in the file's tree,
// and do things by local tree traversal.
//
// However, it's a lot simpler (for me, the programmer)
// to store minimal state info,
// and to reconstruct state info using
// a top-down tree traversal in response to each event.
// Actually we do 2 traversals:
// 1) plan phase:
// We see whether every node recoverable,
// and if so compute its "recovery set":
// the set of children from which it can be recovered
// with minimal cost (i.e. network traffic).
// Decide whether each chunk currently on the server needs to remain.
// 2) action phase
// Based on the results of phase 1,
// decide whether to start upload/download of chunks,
// and whether to delete data currently on server
//
void META_CHUNK::recovery_plan() {
vector<DATA_UNIT*> recoverable;
vector<DATA_UNIT*> present;
unsigned int i;
have_unrecoverable_children = false;
// make lists of children in various states
//
for (i=0; i<children.size(); i++) {
DATA_UNIT* c = children[i];
c->in_recovery_set = false;
c->data_needed = false;
c->data_now_present = false;
c->recovery_plan();
switch (c->status) {
case PRESENT:
present.push_back(c);
break;
case RECOVERABLE:
recoverable.push_back(c);
break;
case UNRECOVERABLE:
have_unrecoverable_children = true;
break;
}
}
// based on states of children, decide what state we're in
//
if ((int)(present.size()) >= coding.n) {
status = PRESENT;
sort(present.begin(), present.end(), compare_cost);
present.resize(coding.n);
cost = 0;
for (i=0; i<present.size(); i++) {
DATA_UNIT* c= present[i];
cost += c->cost;
c->in_recovery_set = true;
}
} else if ((int)(present.size() + recoverable.size()) >= coding.n) {
status = RECOVERABLE;
unsigned int j = coding.n - present.size();
sort(recoverable.begin(), recoverable.end(), compare_cost);
cost = 0;
for (i=0; i<present.size(); i++) {
DATA_UNIT* c= present[i];
c->in_recovery_set = true;
}
for (i=0; i<j; i++) {
DATA_UNIT* c= recoverable[i];
c->in_recovery_set = true;
cost += c->cost;
}
} else {
status = UNRECOVERABLE;
}
}
const char* status_str(int status) {
switch (status) {
case PRESENT: return "present";
case RECOVERABLE: return "recoverable";
case UNRECOVERABLE: return "unrecoverable";
}
return "unknown";
}
void CHUNK::recovery_plan() {
if (present_on_server) {
status = PRESENT;
cost = 0;
min_failures = INT_MAX;
} else if (hosts.size() > 0) {
status = RECOVERABLE;
cost = size;
if ((int)(hosts.size()) < policy.replication) {
data_needed = true;
}
min_failures = hosts.size();
} else {
status = UNRECOVERABLE;
min_failures = 0;
}
#ifdef DEBUG_RECOVERY
printf("chunk plan %s: status %s\n", name, status_str(status));
#endif
}
void META_CHUNK::recovery_action() {
unsigned int i;
if (data_now_present) {
status = PRESENT;
}
#ifdef DEBUG_RECOVERY
printf("meta chunk action %s state %s unrec children %d\n",
name, status_str(status), have_unrecoverable_children
);
#endif
for (i=0; i<children.size(); i++) {
DATA_UNIT* c = children[i];
#ifdef DEBUG_RECOVERY
printf(" child %s status %s in rec set %d\n",
c->name, status_str(c->status), c->in_recovery_set
);
#endif
switch (status) {
case PRESENT:
if (c->status == UNRECOVERABLE) {
c->data_now_present = true;
}
break;
case RECOVERABLE:
if (c->in_recovery_set && have_unrecoverable_children) {
c->data_needed = true;
}
break;
case UNRECOVERABLE:
break;
}
c->recovery_action();
}
// because of recovery action, some of our children may have changed
// status and fault tolerance, source may have changed too.
// Recompute them.
//
vector<DATA_UNIT*> recoverable;
vector<DATA_UNIT*> present;
for (i=0; i<children.size(); i++) {
DATA_UNIT* c = children[i];
switch (c->status) {
case PRESENT:
present.push_back(c);
break;
case RECOVERABLE:
recoverable.push_back(c);
break;
}
}
if ((int)(present.size()) >= coding.n) {
status = PRESENT;
min_failures = INT_MAX;
} else if ((int)(present.size() + recoverable.size()) >= coding.n) {
status = RECOVERABLE;
// our min_failures is the least X such that some X host failures
// would make this node unrecoverable
//
sort(recoverable.begin(), recoverable.end(), compare_min_failures);
min_failures = 0;
unsigned int k = coding.n - present.size();
// we'd need to recover K recoverable children
unsigned int j = recoverable.size() - k + 1;
// a loss of J recoverable children would make this impossible
// the loss of J recoverable children would make us unrecoverable
// Sum the min_failures of the J children with smallest min_failures
//
for (i=0; i<j; i++) {
DATA_UNIT* c = recoverable[i];
printf(" Min failures of %s: %d\n", c->name, c->min_failures);
min_failures += c->min_failures;
}
printf(" our min failures: %d\n", min_failures);
}
}
void CHUNK::recovery_action() {
if (data_now_present) {
present_on_server = true;
parent->dfile->disk_usage.sample_inc(
size,
parent->dfile->collecting_stats()
);
status = PRESENT;
}
if (status == PRESENT && (int)(hosts.size()) < policy.replication) {
assign();
}
if (download_in_progress()) {
data_needed = true;
}
#ifdef DEBUG_RECOVERY
printf("chunk action: %s data_needed %d present_on_server %d\n",
name, data_needed, present_on_server
);
#endif
if (data_needed) {
if (!present_on_server) {
start_upload();
}
} else {
if (present_on_server) {
present_on_server = false;
status = RECOVERABLE;
min_failures = policy.replication;
#ifdef EVENT_DEBUG
printf("%s: %s replicated, removing from server\n", now_str(), name);
#endif
parent->dfile->disk_usage.sample_inc(
-size,
parent->dfile->collecting_stats()
);
}
}
}
set<DFILE*> dfiles;
int main(int argc, char** argv) {
// default policy
//
policy.replication = 2;
policy.coding_levels = 1;
policy.codings[0].n = 10;
policy.codings[0].k = 6;
policy.codings[0].m = 16;
policy.codings[0].n_upload = 12;
for (int i=1; i<argc; i++) {
if (!strcmp(argv[i], "--policy")) {
int retval = policy.parse(argv[++i]);
if (retval) exit(1);
} else if (!strcmp(argv[i], "--host_life_mean")) {
params.host_life_mean = atof(argv[++i]);
} else if (!strcmp(argv[i], "--connect_interval")) {
params.connect_interval = atof(argv[++i]);
} else if (!strcmp(argv[i], "--mean_xfer_rate")) {
params.mean_xfer_rate = atof(argv[++i]);
} else if (!strcmp(argv[i], "--file_size")) {
params.file_size = atof(argv[++i]);
} else {
fprintf(stderr, "bad arg %s\n", argv[i]);
exit(1);
}
}
#if 0
HOST_ARRIVAL *h = new HOST_ARRIVAL;
h->t = 0;
sim.insert(h);
#endif
#if 0
for (int i=0; i<500; i++) {
sim.insert(new HOST);
}
#endif
DFILE* dfile = new DFILE(params.file_size);
sim.insert(dfile);
sim.simulate(params.sim_duration);
printf("%s: simulation finished\n", now_str());
dfile->print_stats();
}