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

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Message-ID: <97468.1700129643@warthog.procyon.org.uk>
Date:   Thu, 16 Nov 2023 10:14:03 +0000
From:   David Howells <dhowells@...hat.com>
To:     David Laight <David.Laight@...LAB.COM>
Cc:     dhowells@...hat.com,
        'Linus Torvalds' <torvalds@...ux-foundation.org>,
        Borislav Petkov <bp@...en8.de>,
        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

David Laight <David.Laight@...LAB.COM> wrote:

> On haswell (which is now quite old) both 'rep movsb' and
> 'rep movsq' copy 16 bytes/clock unless the destination
> is 32 byte aligned when they copy 32 bytes/clock.
> Source alignment make no different, neither does byte
> alignment.

I think the i3-4170 cpu I'm using is Haswell.  Does that mean for my
particular cpu, just using inline "rep movsb" is the best choice?

David