Messages in this thread | | | Date | Thu, 18 Feb 2010 10:18:37 +0100 | From | Andreas Petlund <> | Subject | Re: [net-next PATCH v4 2/3] net: TCP thin linear timeouts |
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On 02/18/2010 10:09 AM, Ilpo Järvinen wrote: > On Thu, 18 Feb 2010, Franco Fichtner wrote: > >> Andreas Petlund wrote: >>> On 02/18/2010 09:41 AM, Ilpo Järvinen wrote: >>> >>>> On Wed, 17 Feb 2010, David Miller wrote: >>>> >>>> >>>>> From: Andreas Petlund <apetlund@simula.no> >>>>> Date: Tue, 16 Feb 2010 15:40:41 +0100 >>>>> >>>>> >>>>>> @@ -341,6 +342,8 @@ struct tcp_sock { >>>>>> u16 advmss; /* Advertised MSS >>>>>> */ >>>>>> u8 frto_counter; /* Number of new acks after RTO */ >>>>>> u8 nonagle; /* Disable Nagle algorithm? >>>>>> */ >>>>>> + u8 thin_lto : 1,/* Use linear timeouts for thin >>>>>> streams */ >>>>>> + thin_undef : 7; >>>>>> >>>>> There is now a gap of 3 unused bytes here in this critical >>>>> core TCP socket data structure. >>>>> >>>>> Please either find a way to avoid this hole, or document >>>>> it with a comment. >>>>> >>>> There would be multiple bits free for use in both frto_counter and nonagle >>>> byte. >>>> >>>> >>> >>> I was playing aroud with this setup: >>> >>> ========= >>> u8 nonagle : 4,/* Disable Nagle algorithm? */ >>> thin_lto : 1,/* Use linear timeouts for thin streams */ >>> thin_dupack : 1,/* Fast retransmit on first dupack */ >>> thin_undef : 2; >>> ========= >>> >>> Do you think that would do the trick? >>> >> >> According to Ilpo, it would be ok to reduce both ftro_counter and >> nonagle, so why not join all these into u16 and leave the remaining >> free bits documented for other people. Like this: >> >> u16 frto_counter:x; /* Number of new acks after RTO */ >> u16 nonagle:y; /* Disable Nagle algorithm? */ >> u16 thin_lto:1; /* Use linear timeouts for thin streams */ >> u16 unused:15-x-y; >> >> Not sure about the y and x. Ilpo, can you comment on those values? > > I don't remember top of the hat how much of nonagle used, but for > frto_counter max value was 3 iirc.
I think nonagle uses 4 bits: ====== #define TCP_NAGLE_OFF 1 /* Nagle's algo is disabled */ #define TCP_NAGLE_CORK 2 /* Socket is corked */ #define TCP_NAGLE_PUSH 4 /* Cork is overridden for already queued data */ ======
> However, I'm unsure if compiler is > nowadays wise enough to handle bitfields in some not all so stupid way.
Would you then recommend to use a byte for each value, thus avoiding the bitfields?
Cheers, Andreas
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