Messages in this thread | | | Subject | Re: 2.6.27-rc5 OLTP performance regression | From | Peter Zijlstra <> | Date | Mon, 08 Sep 2008 20:04:12 +0200 |
| |
On Mon, 2008-09-08 at 20:00 +0200, Peter Zijlstra wrote: > On Mon, 2008-09-08 at 10:58 -0700, Ma, Chinang wrote: > > We found the group scheduler in 2.6.27-rc5 has negative performance > > impact on TPC Online Transaction Processing workload. The test was > > conducted on a dual-socket quad-core Xeon server. OLTP workload is > > disk i/o intensive and we have over 200 database shadow processes > > running in the server during this test. Enabling group scheduler > > (CONFIG_GROUP_SCHED=y) reduced performance by 2.0%. Oprofile data > > indicates significant amount of cycles are spent in tg_shares_up(). > > This is new regression as we did not find the same issue with 2.6.26 > > kernel group scheduler. Is anybody looking into group scheduler > > performance and any idea for reducing the performance impact? > > Because the .26 group scheduler wasn't SMP aware. The extra cost comes > from the fact that .27 is.
What you can do it increase the /proc/sys/kernel/sched_shares_ratelimit value and thereby decrease the accuracy of the SMP fairness of the group scheduler.
| |