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Message-ID: <46688169.8080806@intel.com> Date: Thu, 07 Jun 2007 15:06:33 -0700 From: "Kok, Auke" <auke-jan.h.kok@...el.com> To: hadi@...erus.ca CC: Jeff Garzik <jeff@...zik.org>, David Miller <davem@...emloft.net>, kaber@...sh.net, peter.p.waskiewicz.jr@...el.com, netdev@...r.kernel.org, Jesse Brandeburg <jesse.brandeburg@...el.com> Subject: Re: [PATCH] NET: Multiqueue network device support. jamal wrote: > On Thu, 2007-07-06 at 08:03 -0700, Kok, Auke wrote: >> To prevent against multiple entries bumping head & tail at the same time as well >> as overwriting the same entries in the tx ring (contention for >> next_to_watch/next_to_clean)? > > In current code that lock certainly doesnt protect those specifics. > I thought at some point thats what it did; somehow that seems to have > changed - the rx path/tx prunning is protected by tx_queue_lock > I have tested it the patch on smp and it works. > >> It may be unlikely but ripping out the tx ring >> lock might not be a good idea, perhaps after we get rid of LLTX in e1000? > > I dont think it matters either way. At the moment, you are _guaranteed_ > only one cpu can enter tx path. There may be another CPU, but as long > (as in current code) you dont have any contention between tx and rx, it > seems to be a non-issue. > >> to be honest: I'm open for ideas and I'll give it a try, but stuff like this >> needs to go through some nasty stress testing (multiple clients, long time) >> before I will consider it seriously, but fortunately that's something I can do. > > I empathize but take a closer look; seems mostly useless. > And like i said I have done a quick test with an SMP machine and it > seems to work fine; but your tests will probably be more thorough. the contention isn't between multiple tx attempts, but between e1000_clean and tx. You'll need bidirectional traffic with multiple clients probably to hit it... Auke - 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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