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

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Message-ID: <CAPcyv4jWnaF6tNfZqf13WnqZ0=U98X-5K-kMWnruQPoBYO21KQ@mail.gmail.com>
Date:	Tue, 22 Apr 2014 10:11:56 -0700
From:	Dan Williams <dan.j.williams@...el.com>
To:	Jet Chen <jet.chen@...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 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?

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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