Date: Mon, 20 Aug 2012 06:58:28 -0700 From: Matthew Jacob <mj@feral.com> To: John Baldwin <jhb@freebsd.org> Cc: Poul-Henning Kamp <phk@phk.freebsd.dk>, freebsd-current@freebsd.org, Matt Jacob <mjacob@freebsd.org> Subject: Re: BUFSIZ = 1024, still ? Message-ID: <50324284.2080305@feral.com> In-Reply-To: <201208200824.38500.jhb@freebsd.org> References: <6800.1345323911@critter.freebsd.dk> <201208200824.38500.jhb@freebsd.org>
next in thread | previous in thread | raw e-mail | index | archive | help
On 8/20/2012 5:24 AM, John Baldwin wrote:
> On Saturday, August 18, 2012 5:05:11 pm Poul-Henning Kamp wrote:
>> In message <5030033B.4060705@feral.com>, Matthew Jacob writes:
>>> On 8/18/2012 1:32 PM, Poul-Henning Kamp wrote:
>>>> Shouldn't we at least increase it to pagesize ?
>>>>
>>> What data suggests to you it would be better at pagesize?
>> The number of system calls to fwrite() a big file ?
> Have you looked at an actual ktrace? :) stdio doesn't use BUFSIZ for
> regular files:
>
> head/lib/libc/stdio/makebuf.c:
> /*
> * Internal routine to determine `proper' buffering for a file.
> */
> int
> __swhatbuf(fp, bufsize, couldbetty)
> FILE *fp;
> size_t *bufsize;
> int *couldbetty;
> {
> struct stat st;
>
> if (fp->_file < 0 || _fstat(fp->_file, &st) < 0) {
> ...
> *bufsize = BUFSIZ;
> return (__SNPT);
> }
>
> ...
> if (st.st_blksize <= 0) {
> *bufsize = BUFSIZ;
> return (__SNPT);
> }
>
> *bufsize = st.st_blksize;
> ...
> }
>
> For a regular file stdio will use the filesystem's block size, not BUFSIZ.
>
> Test program:
>
> #include <stdio.h>
> #include <err.h>
>
> int
> main(int ac, char **av)
> {
> char junk;
> FILE *fp;
> int i;
>
> fp = fopen("/tmp/junk", "w");
> if (fp == NULL)
> err(1, "fopen");
> for (i = 0; i < 1024 * 1024; i++)
> if (fwrite(&junk, sizeof(junk), 1, fp) != 1)
> errx(1, "fwrite failed");
> return (0);
> }
>
> ktrace excerpt:
>
> 42599 a.out CALL write(0x3,0x800a04000,0x4000)
> 42599 a.out RET write 16384/0x4000
> 42599 a.out CALL write(0x3,0x800a04000,0x4000)
> 42599 a.out RET write 16384/0x4000
> 42599 a.out CALL write(0x3,0x800a04000,0x4000)
> 42599 a.out RET write 16384/0x4000
> 42599 a.out CALL write(0x3,0x800a04000,0x4000)
> 42599 a.out RET write 16384/0x4000
> 42599 a.out CALL write(0x3,0x800a04000,0x4000)
> 42599 a.out RET write 16384/0x4000
> 42599 a.out CALL write(0x3,0x800a04000,0x4000)
> 42599 a.out RET write 16384/0x4000
>
> This hint also works for pipes (they set st_blksize to PAGE_SIZE). Given
> that, I think BUFSIZ should just be left alone.
>
Perfect. Data.
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?50324284.2080305>