linux-kernel - RE: Mainline kernel OLTP performance update

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Date:	Mon, 19 Jan 2009 13:04:51 -0500
From:	Chris Mason <chris.mason@...cle.com>
To:	"Ma, Chinang" <chinang.ma@...el.com>
Cc:	Steven Rostedt <srostedt@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Matthew Wilcox <matthew@....cx>,
	"Wilcox, Matthew R" <matthew.r.wilcox@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Tripathi, Sharad C" <sharad.c.tripathi@...el.com>,
	"arjan@...ux.intel.com" <arjan@...ux.intel.com>,
	"Kleen, Andi" <andi.kleen@...el.com>,
	"Siddha, Suresh B" <suresh.b.siddha@...el.com>,
	"Chilukuri, Harita" <harita.chilukuri@...el.com>,
	"Styner, Douglas W" <douglas.w.styner@...el.com>,
	"Wang, Peter Xihong" <peter.xihong.wang@...el.com>,
	"Nueckel, Hubert" <hubert.nueckel@...el.com>,
	"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
	Andrew Vasquez <andrew.vasquez@...gic.com>,
	Anirban Chakraborty <anirban.chakraborty@...gic.com>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Gregory Haskins <ghaskins@...ell.com>
Subject: RE: Mainline kernel OLTP performance update

On Thu, 2009-01-15 at 00:11 -0700, Ma, Chinang wrote:
> >> > > > >
> >> > > > > Linux OLTP Performance summary
> >> > > > > Kernel#            Speedup(x)   Intr/s  CtxSw/s us%  sys%   idle%
> >iowait%
> >> > > > > 2.6.24.2                1.000   21969   43425   76   24     0
> >0
> >> > > > > 2.6.27.2                0.973   30402   43523   74   25     0
> >1
> >> > > > > 2.6.29-rc1              0.965   30331   41970   74   26     0
> >0
> >> >
> >> > > But the interrupt rate went through the roof.
> >> >
> >> > Yes.  I forget why that was; I'll have to dig through my archives for
> >> > that.
> >>
> >> Oh.  I'd have thought that this alone could account for 3.5%.

A later email indicated the reschedule interrupt count doubled since
2.6.24, and so I poked around a bit at the causes of resched_task.

I think the -rt version of check_preempt_equal_prio has gotten much more
expensive since 2.6.24.

I'm sure these changes were made for good reasons, and this workload may
not be a good reason to change it back.  But, what does the patch below
do to performance on 2.6.29-rcX?

-chris

diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
index 954e1a8..bbe3492 100644
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -842,6 +842,7 @@ static void check_preempt_curr_rt(struct rq *rq,
struct task_struct *p, int sync
 		resched_task(rq->curr);
 		return;
 	}
+	return;
 
 #ifdef CONFIG_SMP
 	/*




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