linux-kernel - RE: [linus:master] [iov_iter] c9eec08bac: vm-scalability.throughput -16.9% regression

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Message-ID: <ef760f3b926747598051c848ba85c4a8@AcuMS.aculab.com>
Date:   Thu, 16 Nov 2023 16:58:44 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Linus Torvalds' <torvalds@...ux-foundation.org>,
        Borislav Petkov <bp@...en8.de>
CC:     David Howells <dhowells@...hat.com>,
        kernel test robot <oliver.sang@...el.com>,
        "oe-lkp@...ts.linux.dev" <oe-lkp@...ts.linux.dev>,
        "lkp@...el.com" <lkp@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Christian Brauner <brauner@...nel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Jens Axboe <axboe@...nel.dk>, Christoph Hellwig <hch@....de>,
        Christian Brauner <christian@...uner.io>,
        Matthew Wilcox <willy@...radead.org>,
        "ying.huang@...el.com" <ying.huang@...el.com>,
        "feng.tang@...el.com" <feng.tang@...el.com>,
        "fengwei.yin@...el.com" <fengwei.yin@...el.com>
Subject: RE: [linus:master] [iov_iter] c9eec08bac: vm-scalability.throughput
 -16.9% regression

...
> Of course, it's also possible that with all the function call overhead
> introduced by the CPU mitigations on older CPU's, we should just say
> "rep movsb" is always correct - if you have a new CPU with FSRM it's
> good, and if you have an old CPU it's no worse than the horrendous CPU
> mitigation overhead for function call/returns.

Unless you are stupid enough to use a P4 :-)

I actually doubt anyone cares (esp. for 64bit) about any
cpu that don't optimise long 'rep movsb' (pre sandy bridge).

	David

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