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throttle: make throttle_config(throttle_get_config()) symmetric 

Throttling has a weird property that throttle_get_config() does not
always return the same throttling settings that were given with
throttle_config().  In other words, the set and get functions aren't
symmetric.

If .max is 0 then the throttling code assigns a default value of .avg /
10 in throttle_config().  This is an implementation detail of the
throttling algorithm.  When throttle_get_config() is called the .max
value returned should still be 0.

Users are exposed to this quirk via "info block" or "query-block"
monitor commands.  This has caused confusion because it looks like a bug
when an unexpected value is reported.

This patch hides the .max value adjustment in throttle_get_config() and
updates test-throttle.c appropriately.

Reported-by: Nini Gu <ngu@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Message-id: 20170301115026.22621-4-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2017-03-01 11:50:26 +00:00
parent ab08aec45f
commit d72915c60b
2 changed files with 18 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
tests/test-throttle.c
View File

@ -205,8 +205,8 @@ static void test_config_functions(void)
orig_cfg.buckets[THROTTLE_OPS_READ].avg = 69;
orig_cfg.buckets[THROTTLE_OPS_WRITE].avg = 23;
orig_cfg.buckets[THROTTLE_BPS_TOTAL].max = 0; /* should be corrected */
orig_cfg.buckets[THROTTLE_BPS_READ].max = 56; /* should not be corrected */
orig_cfg.buckets[THROTTLE_BPS_TOTAL].max = 0;
orig_cfg.buckets[THROTTLE_BPS_READ].max = 56;
orig_cfg.buckets[THROTTLE_BPS_WRITE].max = 120;
orig_cfg.buckets[THROTTLE_OPS_TOTAL].max = 150;
@ -246,8 +246,8 @@ static void test_config_functions(void)
g_assert(final_cfg.buckets[THROTTLE_OPS_READ].avg == 69);
g_assert(final_cfg.buckets[THROTTLE_OPS_WRITE].avg == 23);
g_assert(final_cfg.buckets[THROTTLE_BPS_TOTAL].max == 15.3); /* fixed */
g_assert(final_cfg.buckets[THROTTLE_BPS_READ].max == 56); /* not fixed */
g_assert(final_cfg.buckets[THROTTLE_BPS_TOTAL].max == 0);
g_assert(final_cfg.buckets[THROTTLE_BPS_READ].max == 56);
g_assert(final_cfg.buckets[THROTTLE_BPS_WRITE].max == 120);
g_assert(final_cfg.buckets[THROTTLE_OPS_TOTAL].max == 150);

14
util/throttle.c
View File

@ -380,6 +380,14 @@ static void throttle_fix_bucket(LeakyBucket *bkt)
}
}
/* undo internal bucket parameter changes (see throttle_fix_bucket()) */
static void throttle_unfix_bucket(LeakyBucket *bkt)
{
if (bkt->max < bkt->avg) {
bkt->max = 0;
}
}
/* take care of canceling a timer */
static void throttle_cancel_timer(QEMUTimer *timer)
{
@ -420,7 +428,13 @@ void throttle_config(ThrottleState *ts,
*/
void throttle_get_config(ThrottleState *ts, ThrottleConfig *cfg)
{
int i;
*cfg = ts->cfg;
for (i = 0; i < BUCKETS_COUNT; i++) {
throttle_unfix_bucket(&cfg->buckets[i]);
}
}