Re: [PATCH] tcp: splice as many packets as possible at once

David Miller
2009-01-08T21:55:28Z

From: Ben Mansell <ben@zeus.com>
Date: Thu, 08 Jan 2009 21:50:44 +0000

> > From fafe76713523c8e9767805cfdc7b73323d7bf180 Mon Sep 17 00:00:00 2001
> > From: Willy Tarreau <w@1wt.eu>
> > Date: Thu, 8 Jan 2009 17:10:13 +0100
> > Subject: [PATCH] tcp: splice as many packets as possible at once
> > Currently, in non-blocking mode, tcp_splice_read() returns after
> > splicing one segment regardless of the len argument. This results
> > in low performance and very high overhead due to syscall rate when
> > splicing from interfaces which do not support LRO.
> > The fix simply consists in not breaking out of the loop after the
> > first read. That way, we can read up to the size requested by the
> > caller and still return when there is no data left.
> > Performance has significantly improved with this fix, with the
> > number of calls to splice() divided by about 20, and CPU usage
> > dropped from 100% to 75%.
> >
>
> I get similar results with my testing here. Benchmarking an application with this patch shows that more than one packet is being splice()d in at once, as a result I see a doubling in throughput.
>
> Tested-by: Ben Mansell <ben@zeus.com>

I'm not applying this until someone explains to me why
we should remove this test from the splice receive but
keep it in the tcp_recvmsg() code where it has been
essentially forever.