Date: Mon, 20 Oct 2008 16:13:25 +0200 From: Mel <fbsd.hackers@rachie.is-a-geek.net> To: freebsd-hackers@freebsd.org Cc: Dan Nelson <dnelson@allantgroup.com>, Ivan Voras <ivoras@freebsd.org> Subject: Re: Pipes, cat buffer size Message-ID: <200810201613.25864.fbsd.hackers@rachie.is-a-geek.net> In-Reply-To: <20081019005021.GN99270@dan.emsphone.com> References: <gddjoj$apg$1@ger.gmane.org> <9bbcef730810181719x4387a14yec74bdb6893d1a2a@mail.gmail.com> <20081019005021.GN99270@dan.emsphone.com>
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On Sunday 19 October 2008 02:50:22 Dan Nelson wrote:
> > But if it works in general, it may simply be that it isn't really
> > applicable to my purpose (and I should modify the reader to read
> > multiple blocks).
>
> That's my suggestion, yes. That way your program would also work when
> passed data from an internet socket (where you will get varying read()
> sizes too). It wouldn't add more than 10 lines to wrap your read in a
> loop that exits when your preferred size has been reached.
Since you mention a socket, would this patch be a good idea and use kqueue to
read from the pipe?
I would think that having the kernel fill the buffer, rather then a busy loop
kernel/userland would improve speed, but I'm not too familiar with the code
to know if this causes any problems.
diff -u -r1.191.2.3 sys_pipe.c
--- sys_pipe.c 6 Jun 2008 12:17:28 -0000 1.191.2.3
+++ sys_pipe.c 20 Oct 2008 14:04:18 -0000
@@ -1594,7 +1609,10 @@
PIPE_UNLOCK(rpipe);
return (1);
}
- ret = kn->kn_data > 0;
+ if ( kn->kn_sfflags & NOTE_LOWAT)
+ ret = kn->kn_data >= kn->kn_sdata;
+ else
+ ret = kn->kn_data > 0;
PIPE_UNLOCK(rpipe);
return ret;
}
--
Mel
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