Messages in this thread | | | Date | Fri, 09 Jan 2009 23:45:02 +0100 | From | Eric Dumazet <> | Subject | Re: [PATCH] tcp: splice as many packets as possible at once |
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Willy Tarreau a écrit : > On Fri, Jan 09, 2009 at 11:12:09PM +0100, Eric Dumazet wrote: >> Willy Tarreau a écrit : >>> On Fri, Jan 09, 2009 at 10:24:00PM +0100, Willy Tarreau wrote: >>>> On Fri, Jan 09, 2009 at 09:51:17PM +0100, Eric Dumazet wrote: >>>> (...) >>>>>> Also, in your second mail, you're saying that your change >>>>>> might return more data than requested by the user. I can't >>>>>> find why, could you please explain to me, as I'm still quite >>>>>> ignorant in this area ? >>>>> Well, I just tested various user programs and indeed got this >>>>> strange result : >>>>> >>>>> Here I call splice() with len=1000 (0x3e8), and you can see >>>>> it gives a result of 1460 at the second call. >>> OK finally I could reproduce it and found why we have this. It's >>> expected in fact. >>> >>> The problem when we loop in tcp_read_sock() is that tss->len is >>> not decremented by the amount of bytes read, this one is done >>> only in tcp_splice_read() which is outer. >>> >>> The solution I found was to do just like other callers, which means >>> use desc->count to keep the remaining number of bytes we want to >>> read. In fact, tcp_read_sock() is designed to use that one as a stop >>> condition, which explains why you first had to hide it. >>> >>> Now with the attached patch as a replacement for my previous one, >>> both issues are solved : >>> - I splice 1000 bytes if I ask to do so >>> - I splice as much as possible if available (typically 23 kB). >>> >>> My observed performances are still at the top of earlier results >>> and IMHO that way of counting bytes makes sense for an actor called >>> from tcp_read_sock(). >>> >>> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c >>> index 35bcddf..51ff3aa 100644 >>> --- a/net/ipv4/tcp.c >>> +++ b/net/ipv4/tcp.c >>> @@ -522,8 +522,12 @@ static int tcp_splice_data_recv(read_descriptor_t *rd_desc, struct sk_buff *skb, >>> unsigned int offset, size_t len) >>> { >>> struct tcp_splice_state *tss = rd_desc->arg.data; >>> + int ret; >>> >>> - return skb_splice_bits(skb, offset, tss->pipe, tss->len, tss->flags); >>> + ret = skb_splice_bits(skb, offset, tss->pipe, rd_desc->count, tss->flags); >>> + if (ret > 0) >>> + rd_desc->count -= ret; >>> + return ret; >>> } >>> >>> static int __tcp_splice_read(struct sock *sk, struct tcp_splice_state *tss) >>> @@ -531,6 +535,7 @@ static int __tcp_splice_read(struct sock *sk, struct tcp_splice_state *tss) >>> /* Store TCP splice context information in read_descriptor_t. */ >>> read_descriptor_t rd_desc = { >>> .arg.data = tss, >>> + .count = tss->len, >>> }; >>> >>> return tcp_read_sock(sk, &rd_desc, tcp_splice_data_recv); >>> >> OK, I came to a different patch. Please check other tcp_read_sock() callers in tree :) > > I've seen the other callers, but they all use desc->count for their own > purpose. That's how I understood what it was used for :-)
Ah yes, I reread your patch and you are right.
> > I think it's better not to change the API here and use tcp_read_sock() > how it's supposed to be used. Also, the less parameters to the function, > the better. > > However I'm OK for the !timeo before release_sock/lock_sock. I just > don't know if we can put the rest of the if above or not. I don't > know what changes we're supposed to collect by doing release_sock/ > lock_sock before the if().
Only the (!timeo) can be above. Other conditions must be checked after the release/lock.
Thank you
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