On Fri, 2015-08-07 at 18:31 +0000, Jason Baron wrote: > From: Jason Baron <jba...@akamai.com> > > When SO_SNDBUF is set and we are under tcp memory pressure, the effective > write > buffer space can be much lower than what was set using SO_SNDBUF. For example, > we may have set the buffer to 100kb, but we may only be able to write 10kb. In > this scenario poll()/select()/epoll(), are going to continuously return > POLLOUT, > followed by -EAGAIN from write() in a very tight loop. > > Introduce sk->sk_effective_sndbuf, such that we can track the 'effective' size > of the sndbuf, when we have a short write due to memory pressure. By using the > sk->sk_effective_sndbuf instead of the sk->sk_sndbuf when we are under memory > pressure, we can delay the POLLOUT until 1/3 of the buffer clears as we > normally > do. There is no issue here when SO_SNDBUF is not set, since the tcp layer will > auto tune the sk->sndbuf. > > In my testing, this brought a single threaad's cpu usage down from 100% to 1% > while maintaining the same level of throughput when under memory pressure. >
I am not sure we need to grow socket for something that looks like a flag ? Also you add a race in sk_stream_wspace() as sk_effective_sndbuf value can change under us. + if (sk->sk_effective_sndbuf) + return sk->sk_effective_sndbuf - sk->sk_wmem_queued; + -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
