netdev - Re: [PATCH] rps: send IPIs ASAP

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Tue, 20 Apr 2010 07:45:51 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Tom Herbert <therbert@...gle.com>
Cc:	Changli Gao <xiaosuo@...il.com>,
	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH] rps: send IPIs ASAP

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.

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



--
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