Stephen Hemminger wrote:
On Fri, 28 Sep 2007 00:08:33 +0200
Eric Dumazet <[EMAIL PROTECTED]> wrote:
Hi all
I am sure some of you are going to tell me that prequeue is not
all black :)
Thank you
[RFC] Make TCP prequeue configurable
The TCP prequeue thing is based on old facts, and has drawbacks.
1) It adds 48 bytes per 'struct tcp_sock'
2) It adds some ugly code in hot paths
3) It has a small hit ratio on typical servers using many sockets
4) It may have a high hit ratio on UP machines running one process,
where the prequeue adds litle gain. (In fact, letting the user
doing the copy after being woke up is better for cache reuse)
5) Doing a copy to user in softirq handler is not good, because of
potential page faults :(
6) Maybe the NET_DMA thing is the only thing that might need prequeue.
This patch introduces a CONFIG_TCP_PREQUEUE, automatically selected if
CONFIG_NET_DMA is on.
Signed-off-by: Eric Dumazet <[EMAIL PROTECTED]>
Rather than having a two more compile cases and test cases to deal
with. If you can prove it is useless, make a case for killing
it completely.
I think it really does help in case (4) with old NICs that don't do rx
checksumming. I'm not sure how many people really care about this
anymore, but probably some...?
OTOH, it would be nice to get rid of sysctl_tcp_low_latency.
-John
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