From: Jon Hunter <jonathanh@nvidia.com>
To: Ashish Mhetre <amhetre@nvidia.com>, <mark.rutland@arm.com>,
<linux-arm-kernel@lists.infradead.org>,
<linux-tegra@vger.kernel.org>, <avanbrunt@nvidia.com>
Cc: <linux-kernel@vger.kernel.org>, <vdumpa@nvidia.com>, <Snikam@nvidia.com>
Subject: Re: [PATCH V3] arm64: Don't flush tlb while clearing the accessed bit
Date: Mon, 29 Oct 2018 09:57:04 +0000 [thread overview]
Message-ID: <b014451f-d81e-1d02-4b04-f719bca6621d@nvidia.com> (raw)
In-Reply-To: <1540805158-618-1-git-send-email-amhetre@nvidia.com>
On 29/10/2018 09:25, Ashish Mhetre wrote:
> From: Alex Van Brunt <avanbrunt@nvidia.com>
>
> Accessed bit is used to age a page and in generic implementation there is
> flush_tlb while clearing the accessed bit.
> Flushing a TLB is overhead on ARM64 as access flag faults don't get
> translation table entries cached into TLB's. Flushing TLB is not necessary
> for this. Clearing the accessed bit without flushing TLB doesn't cause data
> corruption on ARM64.
> In our case with this patch, speed of reading from fast NVMe/SSD through
> PCIe got improved by 10% ~ 15% and writing got improved by 20% ~ 40%.
> So for performance optimisation don't flush TLB when clearing the accessed
> bit on ARM64.
> x86 made the same optimization even though their TLB invalidate is much
> faster as it doesn't broadcast to other CPUs.
> Please refer to:
> 'commit b13b1d2d8692 ("x86/mm: In the PTE swapout page reclaim case clear
> the accessed bit instead of flushing the TLB")'
>
> Signed-off-by: Alex Van Brunt <avanbrunt@nvidia.com>
> Signed-off-by: Ashish Mhetre <amhetre@nvidia.com>
> ---
Please make sure you state here below the above line what has been
changed between each version of the patch.
Thanks
Jon
--
nvpublic
next prev parent reply other threads:[~2018-10-29 9:57 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-29 9:25 [PATCH V3] arm64: Don't flush tlb while clearing the accessed bit Ashish Mhetre
2018-10-29 9:57 ` Jon Hunter [this message]
2018-10-29 10:55 ` Will Deacon
2018-10-29 15:13 ` Alexander Van Brunt
2018-12-03 21:20 ` Alexander Van Brunt
2018-12-06 19:18 ` Will Deacon
[not found] ` <BYAPR12MB271239AAF4A0B79D756850C6CFA90@BYAPR12MB2712.namprd12.prod.outlook.com>
2018-12-06 20:42 ` Alexander Van Brunt
2018-12-07 17:53 ` Will Deacon
2018-12-08 0:05 ` Alexander Van Brunt
[not found] ` <4bac3ba7-a005-213d-5ae4-c0e2ee589d5d@nvidia.com>
2018-10-30 11:50 ` Will Deacon
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