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Date:      Tue, 23 Sep 2025 11:50:49 +0200
From:      Mateusz Guzik <mjguzik@gmail.com>
To:        Konstantin Belousov <kostikbel@gmail.com>
Cc:        John Baldwin <jhb@freebsd.org>, src-committers@freebsd.org,  dev-commits-src-all@freebsd.org, dev-commits-src-main@freebsd.org
Subject:   Re: git: 40a42785dbba - main - fcntl(F_SETFL): only allow one thread to perform F_SETFL
Message-ID:  <CAGudoHHNPXJSrdXwTgQBbGcdRj0mfUUywmcPVaeAO=5-FJ1=zg@mail.gmail.com>
In-Reply-To: <aNG6Cwgb3nPgw6J0@kib.kiev.ua>
References:  <202509191419.58JEJsvj031867@gitrepo.freebsd.org> <92831372-745d-4612-b38f-aeb235dd8cca@FreeBSD.org> <CAGudoHGZs3iOLmbRBwhanNHtDRmd5BE%2Buorq8onCAbCkFw39iw@mail.gmail.com> <ac66d750-3daa-47c6-8b97-51bb69f9a88a@FreeBSD.org> <CAGudoHEMeDzTUBrFo1Gzzq-NhGOkOS0U_-JcfZS_ukKRZYt9XQ@mail.gmail.com> <a66cd016-2198-42e1-85d7-ae46ee10deb3@FreeBSD.org> <aNG6Cwgb3nPgw6J0@kib.kiev.ua>

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On Mon, Sep 22, 2025 at 11:05=E2=80=AFPM Konstantin Belousov
<kostikbel@gmail.com> wrote:
>
> > On 9/22/25 13:40, Mateusz Guzik wrote:
> > > Per my previous e-mail the offset lock is already contested.
> I am curious how they are?
> If several threads do read(2)/write(2) kind of io on the same fd,
> they get what they deserve.
>

I don't know who, I had seen them with poudriere:
https://people.freebsd.org/~mjg/poudriere-offcpu-32kpkg.svg?s=3Dvofflock

Note the % would be higher if it was not for other problems.

> > >
> > > Using a pool over a lock embedded into the struct would hinder perfor=
mance.
> > >
> > > I explained why I don't consider embedding sx into struct file to be =
a problem.
>
> Are you saying that struct file falls into 128-byte zone, and has enough
> space for sx?

It is 80 bytes now. adding 32 still leaves 16 bytes free.



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