Date: Sun, 19 Oct 2008 00:04:51 +0200 From: Ivan Voras <ivoras@freebsd.org> To: freebsd-hackers@freebsd.org Subject: Re: Pipes, cat buffer size Message-ID: <gddmip$im0$1@ger.gmane.org> In-Reply-To: <20081018213502.GL99270@dan.emsphone.com> References: <gddjoj$apg$1@ger.gmane.org> <20081018213502.GL99270@dan.emsphone.com>
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This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enig0322905A6EC536F1489FB784 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Dan Nelson wrote: > In the last episode (Oct 18), Ivan Voras said: >> I'm working on a program that's intended to be used as a "filter", as >> in "something | myprogram > file". I'm trying it with cat and I'm >> seeing my read()s return small blocks, 64 kB in size. I suppose this >> is because cat writes in 64 kB blocks. So: >> >> a) Is there a way to programatically, per-process, set the pipe buffer= >> size? The program in question is a compressor and it's particularly >> inefficient when given small blocks and I'm wondering if the system ca= n >> buffer enough data for it. >=20 > Why not keep reading until you reach your desired compression block > size? Bzip2's default blocksize is 900k, for example. Of course. But that's not the point :) From what I see (didn't look at the code), Linux for example does some kind of internal buffering that decouples how the reader and the writer interact. I think that with FreeBSD's current behaviour the writer could write 1-byte buffers and the reader will be forced to read each byte individually. I don't know if there's some ulterior reason for this. >> b) Is there any objection to the following patch to cat: >=20 > It might be simpler to just use "dd if=3Dmyfile obs=3D1m" instead of > patching cat. I believe patching cat to bring its block size into the century of the fruitbat has its own benefits. --------------enig0322905A6EC536F1489FB784 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (MingW32) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iEYEARECAAYFAkj6XYkACgkQldnAQVacBchVhACeLs1vVbYU6sYy/6yKGAyvEAV7 WFwAn2rzKZxmt1rRJIjJcMI9KHFQoVaT =ncjE -----END PGP SIGNATURE----- --------------enig0322905A6EC536F1489FB784--
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