Messages in this thread | | | Date | Tue, 13 Jan 2009 12:37:02 -0800 | From | Andrew Morton <> | Subject | Re: maximum buffer size for splice(2) tcp->pipe? |
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(cc's added)
On Thu, 8 Jan 2009 11:13:51 +0100 Volker Lendecke <Volker.Lendecke@SerNet.DE> wrote:
> Hi! > > While implementing splice support in Samba for better > performance I found it blocking when trying to pull data off > tcp into a pipe when the recvq was full. Attached find a > test program that shows this behaviour, on another host I > started > > netcat 192.168.19.10 4711 < /dev/zero > > vlendec@lenny:~$ uname -a > Linux lenny 2.6.28-06857-g5cbd04a #7 Wed Jan 7 10:10:42 CET 2009 x86_64 = GNU/Linux > vlendec@lenny:~$ gcc -o splicetest /host/home/vlendec/splicetest.c -O3 -Wall > vlendec@lenny:~$ ./splicetest out 65536 & > [1] 697 > vlendec@lenny:~$ strace -p 697 > Process 697 attached - interrupt to quit > splice(0x3, 0, 0x5, 0, 0x56a0, 0x1) = 22176 > splice(0x7, 0, 0x4, 0, 0x10000, 0x1^C <unfinished ...> > Process 697 detached > vlendec@lenny:~$ netstat -nt | grep 4711 > tcp 69272 0 192.168.19.10:4711 192.168.19.1:33773 ESTABLISHED > vlendec@lenny:~$ > > Interestingly, whenever I start the strace, it gets another > chunk of data and then blocks in the next splice call. > > If I start splicetest with a buffer size of 16384 instead of > 65536, it does not block. I could not find a way to ask the > kernel for the tipping point below which it does not block. > > What is a safe buffer size to use with splice? > > BTW, this kernel is from Steve French's linux-cifs.git repo. > > Thanks, > > Volker Lendecke > > Samba Team > > P.S: I'm not subscribed to linux-kernel, so if possible > please CC me directly. If this is inappropriate behaviour, > please give me a quick hint :-) >
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