netdev - Re: "meaningful" spinlock contention when bound to non-intr CPU?

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: Windows password security audit tool. GUI, reports in PDF.

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

Date:	Fri, 2 Feb 2007 20:06:31 +0100
From:	Andi Kleen <ak@...e.de>
To:	Rick Jones <rick.jones2@...com>
Cc:	Linux Network Development list <netdev@...r.kernel.org>
Subject: Re: "meaningful" spinlock contention when bound to non-intr CPU?

> 
> The meta question behind all that would seem to be whether the scheduler 
> should be telling us where to perform the network processing, or should 
> the network processing be telling the scheduler what to do? (eg all my 
> old blathering about IPS vs TOPS in HP-UX...)

That's an unsolved problem.  But past experiments suggest that giving
the scheduler more imperatives than just "use CPUs well" are often net-losses.

I suspect it cannot be completely solved in the general case. 

> Well, yes and no.  If I drop the "burst" and instead have N times more 
> netperf's going, I see the same lock contention situation.  I wasn't 
> expecting to - thinking that if there were then N different processes on 
> each CPU the likelihood of there being a contention on any one socket 
> was low, but it was there just the same.
> 
> That is part of what makes me wonder if there is a race between wakeup 

A race?

> and release of a lock.

You could try with echo 1 > /proc/sys/net/ipv4/tcp_low_latency.
That should change RX locking behaviour significantly.

-Andi
-
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