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From: Ming Lei <ming.lei@redhat.com>
To: Scotty Bauer <sbauer@eng.utah.edu>
Cc: linux-block@vger.kernel.org, lsf-pc@lists.linux-foundation.org,
	linux-nvme@lists.infradead.org, Linux-scsi@vger.kernel.org
Subject: Re: [Lsf-pc] [LSF/MM TOPIC] KPTI effect on IO performance
Date: Thu, 1 Feb 2018 10:35:21 +0800	[thread overview]
Message-ID: <20180201023520.GA23923@ming.t460p> (raw)
In-Reply-To: <d6729ac299e153de259cb8f8af0c888b@eng.utah.edu>

Hi Scotty,

On Wed, Jan 31, 2018 at 11:43:33AM -0700, Scotty Bauer wrote:
> On 2018-01-31 01:23, Ming Lei wrote:
> > Hi All,
> > 
> > After KPTI is merged, there is extra load introduced to context switch
> > between user space and kernel space. It is observed on my laptop that
> > one
> > syscall takes extra ~0.15us[1] compared with 'nopti'.
> > 
> > IO performance is affected too, it is observed that IOPS drops by 32% in
> > my test[2] on null_blk compared with 'nopti':
> > 
> > randread IOPS on latest linus tree:
> > -------------------------------------------------
> > | randread IOPS     | randread IOPS with 'nopti'|
> > ------------------------------------------------
> > | 928K              | 1372K                     |
> > ------------------------------------------------
> > 
> > 
> 
> Do you know if your CPU has PCID? It would be interesting to see these tests
> on older CPUs or older kernels without PCID support.

My CPU has PCID, which can be retrieved via /proc/cpuinfo.

And the above test is run on same kernel binary, and the result is just done
between 'nopti' and no 'nopti' in kernel command line.

Thanks,
Ming
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  reply	other threads:[~2018-02-01  2:35 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-01-31  8:23 [LSF/MM TOPIC] KPTI effect on IO performance Ming Lei
2018-01-31 18:43 ` Scotty Bauer
2018-02-01  2:35   ` Ming Lei [this message]
2018-02-01  3:05   ` [Lsf-pc] " Ming Lei
2018-02-01 21:51 ` Bart Van Assche

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