linux-kernel - Re: [PATCH] f2fs: introduce DEFAULT_IO_TIMEOUT

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Message-ID: <CAMuHMdV5VtR+vgYKcZtvcz16GPp9YLG_ecAeDsiNCreP4rYKjw@mail.gmail.com>
Date:   Thu, 26 Dec 2019 11:43:38 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Vyacheslav Dubeyko <slava@...eyko.com>
Cc:     Chao Yu <yuchao0@...wei.com>, Jaegeuk Kim <jaegeuk@...nel.org>,
        linux-f2fs-devel@...ts.sourceforge.net,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Chao Yu <chao@...nel.org>,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH] f2fs: introduce DEFAULT_IO_TIMEOUT_JIFFIES

Hi Vyacheslav,

On Wed, Dec 25, 2019 at 10:58 AM Vyacheslav Dubeyko <slava@...eyko.com> wrote:
> On Mon, 2019-12-23 at 09:41 +0100, Geert Uytterhoeven wrote:
> > On Mon, Dec 23, 2019 at 5:01 AM Chao Yu <yuchao0@...wei.com> wrote:
> > > As Geert Uytterhoeven reported:
> > >
> > > for parameter HZ/50 in congestion_wait(BLK_RW_ASYNC, HZ/50);
> > >
> > > On some platforms, HZ can be less than 50, then unexpected 0
> > > timeout
> > > jiffies will be set in congestion_wait().
>
> It looks like that HZ could have various value on diferent platforms.
> So, why does it need to divide HZ on 50? Does it really necessary?
> Could it be used HZ only without the division operation?

A timeout of HZ means 1 second.
HZ/50 means 20 ms, but has the risk of being zero, if HZ < 50.

If you want to use a timeout of 20 ms, you best use msecs_to_jiffies(20),
as that takes care of the special cases, and never returns 0.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds