Re: [PATCH] cat,cp,mv,install,split: Set the minimum IO block size used to 256KiB

[Jim Meyering]

On Wed, Feb 28, 2024 at 9:09 AM Pádraig Brady <P@draigbrady.com> wrote:
>  >> On 11/30/23 12:11, Pádraig Brady wrote:
>  >>> Though that will generally give 128K, which is good when processing all
>  >>> of a file,
>  >>> but perhaps overkill when processing just the last part of a file.
>  >>
>  >> The 128 KiB number was computed as being better for apps like 'sed' that
>  >> typically read all or most of the file. 'tail' sometimes behaves that
>  >> way (e.g., 'tail -c +10') and so 'tail' should use 128 KiB in those
>  >> cases. The simplest way to do that is for 'tail' to use 128 KiB all the
>  >> time - that would cost little for uses like plain 'tail' and it could be
>  >> a significant win for uses like 'tail -c +10'.
>  >
>  > Yes I agree we should use io_blksize() in other routines in tail
>  > where we may dump lots of a file. However in this (most common) case
>  > the routine is dealing with the end of a regular file,
>  > so it's probably best to somewhat minimize the amount of data read,
>  > and more directly check the page_size which is issue at hand.
>  > I've pushed the fix at 
> https://github.com/coreutils/coreutils/commit/73d119f4f
>  > where the adjustment (which also corresponds to what we do in wc) is:
>  >
>  >     if (sb->st_size % page_size == 0)
>  >       bufsize = MAX (BUFSIZ, page_size);
>  >
>  > I'll follow up with another patch to address the performance aspect,
>  > which uses io_blksize() where appropriate.
>
> More testing shows that 256KiB does indeed give a 10-20% bump on modern 
> systems.
> Proposed change is attached.

Thanks. Probably worth setting an alarm to check once a year :-)
I think you'll want to change this comment, too:
> /* As of May 2014, 128KiB is determined to be the minimum