linux-kernel - Re: [libata/ahci] 8a4aeec8d2d: +138.4% perf-stat.dTLB-store-misses, +37.2% perf-stat.dTLB-load-misses

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Date:	Wed, 23 Apr 2014 16:21:06 +0800
From:	Jet Chen <jet.chen@...el.com>
To:	Dan Williams <dan.j.williams@...el.com>
CC:	Tejun Heo <tj@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
	lkp@...org, Fengguang Wu <fengguang.wu@...el.com>
Subject: Re: [libata/ahci] 8a4aeec8d2d: +138.4% perf-stat.dTLB-store-misses,
 +37.2% perf-stat.dTLB-load-misses

On 04/23/2014 01:11 AM, Dan Williams wrote:
> On Mon, Apr 21, 2014 at 12:29 AM, Jet Chen <jet.chen@...el.com> wrote:
>> HI Dan,
>>
>> we noticed the below changes on
>>
>> git://git.kernel.org/pub/scm/linux/kernel/git/tj/libata for-next
>> commit 8a4aeec8d2d6a3edeffbdfae451cdf05cbf0fefd ("libata/ahci: accommodate
>> tag ordered controllers")
> 
> Hi, was this on simulated hardware or a real AHCI controller and disk?
> 

Testing was on a physical machine with a real AHCI controller.

root@bay ~# lspci | grep AHCI
00:1f.2 SATA controller: Intel Corporation 82801IR/IO/IH (ICH9R/DO/DH) 6 port SATA Controller [AHCI mode] (rev 02)

> It does appear this test noticed increased throughput:
> 
>     203893 ~ 0%      +3.7%     211474 ~ 0%  TOTAL iostat.sda.wkB/s
> 
> I wonder if ap->last_tag can be moved to a hotter cacheline, but if
> throughput goes up I can imagine it throws off the cpu statistics
> quite a bit.
> 
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