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List: linux-scsi
Subject: Re: [LSF/MM TOPIC] KPTI effect on IO performance
From: Scotty Bauer <sbauer () eng ! utah ! edu>
Date: 2018-01-31 18:43:33
Message-ID: d6729ac299e153de259cb8f8af0c888b () eng ! utah ! edu
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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.
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