linux-kernel - tbench regression with 2.6.33-rc1

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Date:	Fri, 25 Dec 2009 19:11:07 +0800
From:	Lin Ming <ming.m.lin@...el.com>
To:	peterz@...radead.org, mingo@...e.hu, tglx@...utronix.de
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
Subject: tbench regression with 2.6.33-rc1

Hi,

Test machine: 16 cpus (4P/2Core/HT), 8G mem
tbench test command:
tbench_srv &
tbench 32

Compared with 2.6.32, tbench has ~4% regression in 2.6.33-rc1.

>>From vmstat data, the context switch number also drop ~4%.
perf top data does not show much differences.

But lockstat data shows huge difference in rq->lock, as below.
See the attachment for the full lockstat data.

Any clue of this regression?

Thanks,
Lin Ming

2.6.32
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
                              class name    con-bounces    contentions   waittime-min   waittime-max waittime-total    acq-bounces   acquisitions   holdtime-min   holdtime-max holdtime-total
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

                               &rq->lock:           901            902           1.80          80.65        2402.48          27425       26037113           0.84        4278.44    27119526.04
                               ---------
                               &rq->lock              4          [<ffffffff81036a43>] __sched_setscheduler+0x1c8/0x393
                               &rq->lock            223          [<ffffffff814321c5>] schedule+0xe2/0x830
                               &rq->lock            657          [<ffffffff8103107d>] task_rq_lock+0x39/0x67
                               &rq->lock             16          [<ffffffff8103d2b6>] scheduler_tick+0x3d/0x206
                               ---------
                               &rq->lock            425          [<ffffffff814321c5>] schedule+0xe2/0x830
                               &rq->lock            427          [<ffffffff8103107d>] task_rq_lock+0x39/0x67
                               &rq->lock             20          [<ffffffff8103d2b6>] scheduler_tick+0x3d/0x206
                               &rq->lock              4          [<ffffffff81033292>] double_lock_balance+0x40/0x6a


2.6.33-rc1
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
                              class name    con-bounces    contentions   waittime-min   waittime-max waittime-total    acq-bounces   acquisitions   holdtime-min   holdtime-max holdtime-total
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

                               &rq->lock:          5987           6019           0.00          25.15       20551.87          37851       25873389           0.00        3819.73    29524592.69
                               ---------
                               &rq->lock           5254          [<ffffffff8102a6d9>] task_rq_lock+0x39/0x67
                               &rq->lock            410          [<ffffffff81439c75>] schedule+0xba/0x8ae
                               &rq->lock            336          [<ffffffff8103086f>] try_to_wake_up+0xe3/0x26f
                               &rq->lock             28          [<ffffffff8102c995>] double_lock_balance+0x40/0x6a
                               ---------
                               &rq->lock            468          [<ffffffff8102a6d9>] task_rq_lock+0x39/0x67
                               &rq->lock           5022          [<ffffffff81439c75>] schedule+0xba/0x8ae
                               &rq->lock             13          [<ffffffff81030555>] double_rq_lock+0x40/0x79
                               &rq->lock            477          [<ffffffff8103086f>] try_to_wake_up+0xe3/0x26f


View attachment "lockstat.tbench.2.6.32" of type "text/plain" (185607 bytes)

View attachment "lockstat.tbench.2.6.33-rc1" of type "text/plain" (188330 bytes)