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

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Message-ID: <20231115215917.GKZVU/NXl5BkyCPt/M@fat_crate.local>
Date:   Wed, 15 Nov 2023 22:59:17 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     David Howells <dhowells@...hat.com>,
        kernel test robot <oliver.sang@...el.com>,
        oe-lkp@...ts.linux.dev, lkp@...el.com,
        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>,
        David Laight <David.Laight@...lab.com>, ying.huang@...el.com,
        feng.tang@...el.com, fengwei.yin@...el.com
Subject: Re: [linus:master] [iov_iter] c9eec08bac: vm-scalability.throughput
 -16.9% regression

On Wed, Nov 15, 2023 at 04:50:06PM -0500, Linus Torvalds wrote:
> Sadly, we don't seem to have any obvious #define for "this is not real
> kernel code". We just have a lot of ad-hoc tricks, like removing
> compiler flags and disabling things like KASAN etc on a file-by-file
> (or directory) basis.

Yeah, "untangling" memcpy() has always been a PITA, every time I tried
it. So I'd need to come up with a somewhat sensible scheme of "use this
special memcpy() only in kernel code proper and fallback to the library
version or gcc builtin otherwise"...

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette