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Message-ID: <j2l412e6f7f1004200217h904cf469le35387c350d4d1a2@mail.gmail.com> Date: Tue, 20 Apr 2010 17:17:26 +0800 From: Changli Gao <xiaosuo@...il.com> To: Eric Dumazet <eric.dumazet@...il.com> Cc: Tom Herbert <therbert@...gle.com>, "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org Subject: Re: [PATCH] rps: send IPIs ASAP On Tue, Apr 20, 2010 at 1:45 PM, Eric Dumazet <eric.dumazet@...il.com> wrote: > Le lundi 19 avril 2010 à 22:15 -0700, Tom Herbert a écrit : >> On Mon, Apr 19, 2010 at 9:08 PM, Changli Gao <xiaosuo@...il.com> wrote: >> > rps: send IPIs ASAP >> > >> > In order to reduce latency, we'd better send IPIs ASAP to schedule the >> > corresponding NAPIs. >> > >> A design point of RPS is that we generate at most one IPI per CPU per >> device interrupt, which at least offers some predictable coalescing. >> With your changes, we would get at most one IPI per packet-- that >> could represent a lot more of them. Did you test this to see what the >> impact is in this regard? >> > > I agree with you Tom. Coalescing IPI is probably better. > > If the receiver CPU got a single packet in its RX handling, latency will > be the same anyway. I did the "ping -f" test again, and found that the differences of RTT I got before were noises. It seems your "shortcut net_rps_action()" patch eliminates the differences. > > If the receiver CPU got many packets, chance is high we are in a stress > situation, and coalescing is a win in this case. > > I am currently testing a patch to call net_rps_action() at the beginning > of process_backlog() (if we have a non null ipi_rps_list pointer) > > Will post a patch with bench results > It sounds like a better idea. -- Regards, Changli Gao(xiaosuo@...il.com) -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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