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From: Neeraj Singh <nksingh85@gmail.com>
To: Junio C Hamano <gitster@pobox.com>
Cc: Chris Torek <chris.torek@gmail.com>,
	Jeff Hostetler <git@jeffhostetler.com>,
	Git List <git@vger.kernel.org>,
	"Neeraj K. Singh" <neerajsi@microsoft.com>
Subject: Re: [PATCH] read-cache: make the index write buffer size 128K
Date: Wed, 24 Feb 2021 23:36:20 -0800	[thread overview]
Message-ID: <CANQDOdd+keN3LyC4CHWDZ3JHYurEy_FLyw5GT5UKqg0RcTA+DA@mail.gmail.com> (raw)
In-Reply-To: <xmqqeeh4wrad.fsf@gitster.g>

On Wed, Feb 24, 2021 at 11:16 PM Junio C Hamano <gitster@pobox.com> wrote:
>
> Chris Torek <chris.torek@gmail.com> writes:
>
> > Linux/BSD/etc `stat` system calls report st_blksize values to tell
> > user code the optimal size for read and write calls.  Does Windows
> > have one?  (It's not POSIX but is XSI.)
> >
> > (How *well* the OS reports `st_blksize` is another question
> > entirely, but at least if the report says, say, 128k, and that's
> > wrong, that's no longer Git's fault. :-) )
> > ...
> > 128K is correct for ZFS; 64K is typically correct for UFS2; 8K is
> > the old UFS1 size.  Anything under that has been too small for
> > a long time. :-)
>
> That's rather tempting.  After opening a locked index to write
> things out, the value is a single fstat() away...
>

From a quick perusal of freebsd, st_blksize seems to be the system
PAGE_SIZE by default (4k most of the time, I assume). The Windows
equivalent of this value is really tuned to what you want to send down
when bypassing the cache (to avoid partial cluster/stripe writes).

https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/sys_stat.h.html
doesn't elicit much confidence. The units of st_blksize aren't even
defined.

Thanks,
Neeraj

  reply	other threads:[~2021-02-25  7:47 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-18  2:48 [PATCH] read-cache: make the index write buffer size 128K Neeraj K. Singh via GitGitGadget
2021-02-19 19:12 ` Jeff Hostetler
2021-02-20  3:28   ` Junio C Hamano
2021-02-20  7:56     ` Neeraj Singh
2021-02-21 12:51       ` Junio C Hamano
2021-02-24 20:56         ` Neeraj Singh
2021-02-25  5:41           ` Junio C Hamano
2021-02-25  6:58             ` Chris Torek
2021-02-25  7:16               ` Junio C Hamano
2021-02-25  7:36                 ` Neeraj Singh [this message]
2021-02-25  7:57                   ` Chris Torek

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