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cam iosched: Bettar account IOPS for smoother performance

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Prevent cam_iosched_iops_tick() from discarding 'unspent' ios unless
it's a new accounting interval.

Previously ios that weren't used between ticks were lost, as a result
the iops limiter could enforce a limit below the configured maximum.

Obtained from: ElectroBSD
Submitted by: Fabian Keil
PR: 221974
This commit is contained in:
Warner Losh 2017-09-22 02:36:36 +00:00
parent f777123b83
commit 78ed811e6c
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=323894
1 changed files with 17 additions and 6 deletions
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23
sys/cam/cam_iosched.c
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@ -423,20 +423,31 @@ cam_iosched_iops_init(struct iop_stats *ios)
static int
cam_iosched_iops_tick(struct iop_stats *ios)
{
int new_ios;
if ((ios->softc->total_ticks % ios->softc->quanta) == 0)
ios->l_value2 = 0;
ios->l_value1 = (int)((ios->current * (uint64_t)ios->softc->this_frac) >> 16);
/*
* Allow at least one IO per tick until all
* the IOs for this interval have been spent.
*/
if (ios->l_value1 <= 0 && ios->l_value2 < ios->current) {
ios->l_value1 = 1;
new_ios = (int)((ios->current * (uint64_t)ios->softc->this_frac) >> 16);
if (new_ios < 1 && ios->l_value2 < ios->current) {
new_ios = 1;
ios->l_value2++;
}
/*
* If this a new accounting interval, discard any "unspent" ios
* granted in the previous interval. Otherwise add the new ios to
* the previously granted ones that haven't been spent yet.
*/
if ((ios->softc->total_ticks % ios->softc->quanta) == 0) {
ios->l_value1 = new_ios;
ios->l_value2 = 1;
} else {
ios->l_value1 += new_ios;
}
return 0;
}