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Commit 7950701f authored by Andrew Morton's avatar Andrew Morton Committed by Linus Torvalds
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[PATCH] AS: new process estimation 

From: Nick Piggin <piggin@cyberone.com.au>

This one gathers better statistics about the new process problem.  It
improves estimation for initial process IO.  That is, better calculations
for whether it will be worth waiting after a process submits its first
read.

This is done with a per queue average thinktime and seek time for a second
read submitted from a process.

When combined with 3/3, numbers are around the same as mm1 for most long
lived tasks, but much better for things like the top 4 benchmarks.

Probably wants rwhron and the OSDL database guys to give it some testing.

test                                    2.6.0-test9-mm1  2.6.0-test9-mm1-np
Cat kernel source during seq read       0:26.89          0:24.75
Cat kernel source during seq write      9:17.80          0:23.48
ls -lr kernel source during seq read    0:11.03          0:14.68
ls -lr kernel source during seq write   0:49.95          0:08.06

contest no_load                         143s 0 loads     144s 0 loads
contest io_load                         193s 40.2 loads  193s 40.1 loads
contest read_load                       186s 11.6 loads  190s 10.5 loads
contest list_load                       201s 5.0 loads   200s 5.0 loads

pgbench 1 client                        31.3TPS          31.5TPS
pgbench 4 clients                       37.7TPS          37.5TPS
pgbench 16 clients                      42.1TPS          48.1TPS
parent 766b36ce
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Inline Side-by-side
Showing with 130 additions and 77 deletions
drivers/block/as-iosched.c
View file @ 7950701f
......@@ -70,6 +70,7 @@
/* Bits in as_io_context.state */
enum as_io_states {
AS_TASK_RUNNING=0, /* Process has not exitted */
AS_TASK_IOSTARTED, /* Process has started some IO */
AS_TASK_IORUNNING, /* Process has completed some IO */
};
......@@ -99,6 +100,14 @@ struct as_data {
sector_t last_sector[2]; /* last REQ_SYNC & REQ_ASYNC sectors */
struct list_head *dispatch; /* driver dispatch queue */
struct list_head *hash; /* request hash */
unsigned long exit_prob; /* probability a task will exit while
being waited on */
unsigned long new_ttime_total; /* mean thinktime on new proc */
unsigned long new_ttime_mean;
u64 new_seek_total; /* mean seek on new proc */
sector_t new_seek_mean;
unsigned long current_batch_expires;
unsigned long last_check_fifo[2];
int changed_batch; /* 1: waiting for old batch to end */
......@@ -186,6 +195,7 @@ static void free_as_io_context(struct as_io_context *aic)
/* Called when the task exits */
static void exit_as_io_context(struct as_io_context *aic)
{
WARN_ON(!test_bit(AS_TASK_RUNNING, &aic->state));
clear_bit(AS_TASK_RUNNING, &aic->state);
}
......@@ -608,8 +618,15 @@ static void as_antic_timeout(unsigned long data)
spin_lock_irqsave(q->queue_lock, flags);
if (ad->antic_status == ANTIC_WAIT_REQ
|| ad->antic_status == ANTIC_WAIT_NEXT) {
struct as_io_context *aic = ad->io_context->aic;
ad->antic_status = ANTIC_FINISHED;
kblockd_schedule_work(&ad->antic_work);
if (aic->ttime_samples == 0) {
/* process anticipated on has exitted or timed out*/
ad->exit_prob = (7*ad->exit_prob + 256)/8;
}
}
spin_unlock_irqrestore(q->queue_lock, flags);
}
......@@ -623,7 +640,7 @@ static int as_close_req(struct as_data *ad, struct as_rq *arq)
unsigned long delay; /* milliseconds */
sector_t last = ad->last_sector[ad->batch_data_dir];
sector_t next = arq->request->sector;
sector_t delta; /* acceptable close offset (in sectors) */
sector_t delta; /* acceptable close offset (in sectors) */
if (ad->antic_status == ANTIC_OFF || !ad->ioc_finished)
delay = 0;
......@@ -657,6 +674,15 @@ static int as_can_break_anticipation(struct as_data *ad, struct as_rq *arq)
{
struct io_context *ioc;
struct as_io_context *aic;
sector_t s;
ioc = ad->io_context;
BUG_ON(!ioc);
if (arq && ioc == arq->io_context) {
/* request from same process */
return 1;
}
if (arq && arq->is_sync == REQ_SYNC && as_close_req(ad, arq)) {
/* close request */
......@@ -671,20 +697,14 @@ static int as_can_break_anticipation(struct as_data *ad, struct as_rq *arq)
return 1;
}
ioc = ad->io_context;
BUG_ON(!ioc);
if (arq && ioc == arq->io_context) {
/* request from same process */
return 1;
}
aic = ioc->aic;
if (!aic)
return 0;
if (!test_bit(AS_TASK_RUNNING, &aic->state)) {
/* process anticipated on has exitted */
if (aic->ttime_samples == 0)
ad->exit_prob = (7*ad->exit_prob + 256)/8;
return 1;
}
......@@ -698,27 +718,36 @@ static int as_can_break_anticipation(struct as_data *ad, struct as_rq *arq)
return 1;
}
if (aic->seek_samples == 0 || aic->ttime_samples == 0) {
/*
* Process has just started IO. Don't anticipate.
* TODO! Must fix this up.
*/
return 1;
}
if (aic->ttime_mean > ad->antic_expire) {
if (aic->ttime_samples == 0) {
if (ad->new_ttime_mean > ad->antic_expire)
return 1;
if (ad->exit_prob > 128)
return 1;
} else if (aic->ttime_mean > ad->antic_expire) {
/* the process thinks too much between requests */
return 1;
}
if (arq && aic->seek_samples) {
sector_t s;
if (ad->last_sector[REQ_SYNC] < arq->request->sector)
s = arq->request->sector - ad->last_sector[REQ_SYNC];
else
s = ad->last_sector[REQ_SYNC] - arq->request->sector;
if (!arq)
return 0;
if (ad->last_sector[REQ_SYNC] < arq->request->sector)
s = arq->request->sector - ad->last_sector[REQ_SYNC];
else
s = ad->last_sector[REQ_SYNC] - arq->request->sector;
if (aic->seek_samples == 0) {
/*
* Process has just started IO. Use past statistics to
* guage success possibility
*/
if (ad->new_seek_mean/2 > s) {
/* this request is better than what we're expecting */
return 1;
}
if (aic->seek_mean > (s>>1)) {
} else {
if (aic->seek_mean/2 > s) {
/* this request is better than what we're expecting */
return 1;
}
......@@ -763,12 +792,51 @@ static int as_can_anticipate(struct as_data *ad, struct as_rq *arq)
return 1;
}
static void as_update_thinktime(struct as_data *ad, struct as_io_context *aic, unsigned long ttime)
{
/* fixed point: 1.0 == 1<<8 */
if (aic->ttime_samples == 0) {
ad->new_ttime_total = (7*ad->new_ttime_total + 256*ttime) / 8;
ad->new_ttime_mean = ad->new_ttime_total / 256;
ad->exit_prob = (7*ad->exit_prob)/8;
}
aic->ttime_samples = (7*aic->ttime_samples + 256) / 8;
aic->ttime_total = (7*aic->ttime_total + 256*ttime) / 8;
aic->ttime_mean = (aic->ttime_total + 128) / aic->ttime_samples;
}
static void as_update_seekdist(struct as_data *ad, struct as_io_context *aic, sector_t sdist)
{
u64 total;
if (aic->seek_samples == 0) {
ad->new_seek_total = (7*ad->new_seek_total + 256*(u64)sdist)/8;
ad->new_seek_mean = ad->new_seek_total / 256;
}
/*
* Don't allow the seek distance to get too large from the
* odd fragment, pagein, etc
*/
if (aic->seek_samples <= 60) /* second&third seek */
sdist = min(sdist, (aic->seek_mean * 4) + 2*1024*1024);
else
sdist = min(sdist, (aic->seek_mean * 4) + 2*1024*64);
aic->seek_samples = (7*aic->seek_samples + 256) / 8;
aic->seek_total = (7*aic->seek_total + (u64)256*sdist) / 8;
total = aic->seek_total + (aic->seek_samples/2);
do_div(total, aic->seek_samples);
aic->seek_mean = (sector_t)total;
}
/*
* as_update_iohist keeps a decaying histogram of IO thinktimes, and
* updates @aic->ttime_mean based on that. It is called when a new
* request is queued.
*/
static void as_update_iohist(struct as_io_context *aic, struct request *rq)
static void as_update_iohist(struct as_data *ad, struct as_io_context *aic, struct request *rq)
{
struct as_rq *arq = RQ_DATA(rq);
int data_dir = arq->is_sync;
......@@ -779,60 +847,29 @@ static void as_update_iohist(struct as_io_context *aic, struct request *rq)
return;
if (data_dir == REQ_SYNC) {
unsigned long in_flight = atomic_read(&aic->nr_queued)
+ atomic_read(&aic->nr_dispatched);
spin_lock(&aic->lock);
if (test_bit(AS_TASK_IORUNNING, &aic->state)
&& !atomic_read(&aic->nr_queued)
&& !atomic_read(&aic->nr_dispatched)) {
if (test_bit(AS_TASK_IORUNNING, &aic->state) ||
test_bit(AS_TASK_IOSTARTED, &aic->state)) {
/* Calculate read -> read thinktime */
thinktime = jiffies - aic->last_end_request;
thinktime = min(thinktime, MAX_THINKTIME-1);
/* fixed point: 1.0 == 1<<8 */
aic->ttime_samples += 256;
aic->ttime_total += 256*thinktime;
if (aic->ttime_samples)
/* fixed point factor is cancelled here */
aic->ttime_mean = (aic->ttime_total + 128)
/ aic->ttime_samples;
aic->ttime_samples = (aic->ttime_samples>>1)
+ (aic->ttime_samples>>2);
aic->ttime_total = (aic->ttime_total>>1)
+ (aic->ttime_total>>2);
if (test_bit(AS_TASK_IORUNNING, &aic->state)
&& in_flight == 0) {
thinktime = jiffies - aic->last_end_request;
thinktime = min(thinktime, MAX_THINKTIME-1);
} else
thinktime = 0;
as_update_thinktime(ad, aic, thinktime);
/* Calculate read -> read seek distance */
if (aic->last_request_pos < rq->sector)
seek_dist = rq->sector - aic->last_request_pos;
else
seek_dist = aic->last_request_pos - rq->sector;
as_update_seekdist(ad, aic, seek_dist);
}
/* Calculate read -> read seek distance */
if (!aic->seek_samples)
seek_dist = 0;
else if (aic->last_request_pos < rq->sector)
seek_dist = rq->sector - aic->last_request_pos;
else
seek_dist = aic->last_request_pos - rq->sector;
aic->last_request_pos = rq->sector + rq->nr_sectors;
/*
* Don't allow the seek distance to get too large from the
* odd fragment, pagein, etc
*/
if (aic->seek_samples < 400) /* second&third seek */
seek_dist = min(seek_dist, (aic->seek_mean * 4)
+ 2*1024*1024);
else
seek_dist = min(seek_dist, (aic->seek_mean * 4)
+ 2*1024*64);
aic->seek_samples += 256;
aic->seek_total += (u64)256*seek_dist;
if (aic->seek_samples) {
u64 total = aic->seek_total + (aic->seek_samples>>1);
do_div(total, aic->seek_samples);
aic->seek_mean = (sector_t)total;
}
aic->seek_samples = (aic->seek_samples>>1)
+ (aic->seek_samples>>2);
aic->seek_total = (aic->seek_total>>1)
+ (aic->seek_total>>2);
set_bit(AS_TASK_IOSTARTED, &aic->state);
spin_unlock(&aic->lock);
}
}
......@@ -1376,8 +1413,8 @@ static void as_add_request(struct as_data *ad, struct as_rq *arq)
arq->io_context = as_get_io_context();
if (arq->io_context) {
as_update_iohist(ad, arq->io_context->aic, arq->request);
atomic_inc(&arq->io_context->aic->nr_queued);
as_update_iohist(arq->io_context->aic, arq->request);
}
alias = as_add_arq_rb(ad, arq);
......@@ -1885,6 +1922,17 @@ as_var_store(unsigned long *var, const char *page, size_t count)
return count;
}
static ssize_t as_est_show(struct as_data *ad, char *page)
{
int pos = 0;
pos += sprintf(page+pos, "%lu %% exit probability\n", 100*ad->exit_prob/256);
pos += sprintf(page+pos, "%lu ms new thinktime\n", ad->new_ttime_mean);
pos += sprintf(page+pos, "%llu sectors new seek distance\n", (unsigned long long)ad->new_seek_mean);
return pos;
}
#define SHOW_FUNCTION(__FUNC, __VAR) \
static ssize_t __FUNC(struct as_data *ad, char *page) \
{ \
......@@ -1916,6 +1964,10 @@ STORE_FUNCTION(as_write_batchexpire_store,
&ad->batch_expire[REQ_ASYNC], 0, INT_MAX);
#undef STORE_FUNCTION
static struct as_fs_entry as_est_entry = {
.attr = {.name = "est_time", .mode = S_IRUGO },
.show = as_est_show,
};
static struct as_fs_entry as_readexpire_entry = {
.attr = {.name = "read_expire", .mode = S_IRUGO | S_IWUSR },
.show = as_readexpire_show,
......@@ -1943,6 +1995,7 @@ static struct as_fs_entry as_write_batchexpire_entry = {
};
static struct attribute *default_attrs[] = {
&as_est_entry.attr,
&as_readexpire_entry.attr,
&as_writeexpire_entry.attr,
&as_anticexpire_entry.attr,
......
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