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Message-ID: <CAJgzZorDSoSeSWc4UVSMW+2gNC=uDPZZ_jMDA8XiD8oiCfPp8A@mail.gmail.com>
Date: Tue, 24 Sep 2024 11:56:05 -0400
From: enh <enh@...gle.com>
To: libc-coord@...ts.openwall.com
Cc: Schrodinger ZHU Yifan <i@...yi.fan>
Subject: Re: getrandom via vDSO
ah, glibc has an arc4random() that makes a syscall for _every_ call...
On Tue, Sep 24, 2024 at 3:19 AM Florian Weimer <fweimer@...hat.com> wrote:
> * Schrodinger ZHU Yifan:
>
> > 1 Is there a clear performance demand such that it becomes necessarily
> > to avoid syscall inside getrandom​?
>
> A pure kernelspace implementation of arc4random is unusable for many
> applications due to system call overhead. If that's what libc offers,
> some applications will have to use a bundled userspace implementation
> instead.
>
> Miroslav Lichvar reported a ~25% performance regression if glibc's
> kernel-based arc4random is used:
>
> | The new arc4random using getrandom() seems to have a significant
> | impact on performance of chronyd operating as an NTP server. On an
> | Intel E3-1220 CPU, I see that the maximum number of requests per
> | second dropped by about 25%. That would be an issue for some public
> | NTP servers.
>
> <https://sourceware.org/bugzilla/show_bug.cgi?id=29437>
>
> On newer CPUs, it's likely even worse.
>
> Thanks,
> Florian
>
>
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