netdev - Re: [PATCH] net: reduce net_rx

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]

Message-ID: <1363879647.4431.8.camel@edumazet-glaptop>
Date:	Thu, 21 Mar 2013 08:27:27 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Paul Gortmaker <paul.gortmaker@...driver.com>
Cc:	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>, stable <stable@...r.kernel.org>,
	Willy Tarreau <w@....eu>, Tom Herbert <therbert@...gle.com>
Subject: Re: [PATCH] net: reduce net_rx_action() latency to 2 HZ

On Thu, 2013-03-21 at 11:03 -0400, Paul Gortmaker wrote:
> [CC'ing stable & Willy - for the older releases not fed by
> http://patchwork.ozlabs.org/bundle/davem/stable/ ]
> 
> On Tue, Mar 5, 2013 at 12:15 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> > From: Eric Dumazet <edumazt@...gle.com>
> >
> > We should use time_after_eq() to get maximum latency of two ticks,
> > instead of three.
> >
> > Bug added in commit 24f8b2385 (net: increase receive packet quantum)
> 
> I'm not sure what applications would notice the extra tick, but 24f8b takes
> us back to 2.6.29.  It cherry picks cleanly onto 2.6.34, so it probably also
> does the same for Willy's 2.6.32 longterm too.
> 
> Commit is now mainline d114a3338747255518 - v3.9-rc3~36^2~34.

BQL (Bytes Queue Limit) relies on TX completion being run often, and
Qdisc being serviced often as well. If net_rx_action() hogs the cpu,
net_tx_action() is delayed and NIC can stall.

I wrote this patch because I was investigating a regression when a
Google application began using BQL enabled kernels.

About the latency in itself, following commit is way more interesting.

commit c10d73671ad30f5 (softirq: reduce latencies)

As without it, I could trigger more than 50ms latencies for the poor
user thread interrupted by softirq processing.


--
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