linux-kernel - Re: Bad SSD performance with recent kernels

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Date:	Mon, 30 Jan 2012 13:45:12 +0800
From:	Shaohua Li <shli@...nel.org>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Wu Fengguang <wfg@...ux.intel.com>,
	Herbert Poetzl <herbert@...hfloor.at>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Jens Axboe <axboe@...nel.dk>, Tejun Heo <tj@...nel.org>
Subject: Re: Bad SSD performance with recent kernels

2012/1/30 Eric Dumazet <eric.dumazet@...il.com>:
> Le lundi 30 janvier 2012 à 11:17 +0800, Shaohua Li a écrit :
>
>> 1M block size is slow, I guess it's CPU related.
>>
>> And as for the big regression with newer kernel than 2.6.38, please
>> check if idle=poll
>> helps. CPU idle dramatically impacts disk performance and even latest
>> cpuidle governor
>> doesn't help for some CPUs.
>>
>
> No change with idle=poll
I mean the big regression might be related to CPU idle. because I
saw really bad performance with CPU idle with some CPUs.

The 1M block size performance is lower than 128K is not. but I still
guess it's CPU related (like copy). The test result is always like this
IIRC.
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