From mboxrd@z Thu Jan  1 00:00:00 1970
From: Chris Mason <chris.mason@oracle.com>
Subject: RE: Mainline kernel OLTP performance update
Date: Mon, 19 Jan 2009 13:04:51 -0500
Message-ID: <1232388291.6521.140.camel@think.oraclecorp.com>
References: <BC02C49EEB98354DBA7F5DD76F2A9E800317003CB0@azsmsx501.amr.corp.intel.com>
	 <CAC4B8726E86A142B27A9E9A2F2F12479D3E945F@rrsmsx505.amr.corp.intel.com>
	 <20090114163557.11e097f2.akpm@linux-foundation.org>
	 <20090115012147.GW29283@parisc-linux.org>
	 <20090114180431.f4a96543.akpm@linux-foundation.org>
	 <1231986439.21980.54.camel@localhost.localdomain>
	 <BC02C49EEB98354DBA7F5DD76F2A9E80031752B166@azsmsx501.amr.corp.intel.com>
Mime-Version: 1.0
Content-Type: text/plain
Content-Transfer-Encoding: 7bit
Return-path: <linux-scsi-owner@vger.kernel.org>
Received: from rcsinet11.oracle.com ([148.87.113.123]:31612 "EHLO
	rgminet11.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1751843AbZASSGO (ORCPT
	<rfc822;linux-scsi@vger.kernel.org>); Mon, 19 Jan 2009 13:06:14 -0500
In-Reply-To: <BC02C49EEB98354DBA7F5DD76F2A9E80031752B166@azsmsx501.amr.corp.intel.com>
Sender: linux-scsi-owner@vger.kernel.org
List-Id: linux-scsi@vger.kernel.org
To: "Ma, Chinang" <chinang.ma@intel.com>
Cc: Steven Rostedt <srostedt@redhat.com>, Andrew Morton <akpm@linux-foundation.org>, Matthew Wilcox <matthew@wil.cx>, "Wilcox, Matthew R" <matthew.r.wilcox@intel.com>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, "Tripathi, Sharad C" <sharad.c.tripathi@intel.com>, "arjan@linux.intel.com" <arjan@linux.intel.com>, "Kleen, Andi" <andi.kleen@intel.com>, "Siddha, Suresh B" <suresh.b.siddha@intel.com>, "Chilukuri, Harita" <harita.chilukuri@intel.com>, "Styner, Douglas W" <douglas.w.styner@intel.com>, "Wang, Peter Xihong" <peter.xihong.wang@intel.com>, "Nueckel, Hubert" <hubert.nueckel@intel.com>, "linux-scsi@vger.kernel.org" <linux-scsi@vger.kernel.org>, Andrew Vasquez <andrew.vasquez@qlogic.com>, Anirban Chakraborty <anirban.chakraborty@qlogic.com>, Ingo Molnar <mingo@redhat.com>, Thomas Gleixner <tglx@linutronix.de>, Peter Zijlstra <peterz@infradead.org>

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
 	/*