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From: Roland Dreier <rdreier-FYB4Gu1CFyUAvxtiuMwx3w@public.gmane.org>
To: Bart Van Assche <bvanassche-HInyCGIudOg@public.gmane.org>
Cc: Ralph Campbell
	<ralph.campbell-h88ZbnxC6KDQT0dZR+AlfA@public.gmane.org>,
	linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Subject: Re: [PATCH 2/3] IB/srp: use IB_CQ_REPORT_MISSED_EVENTS to avoid  missed CQ callbacks
Date: Wed, 31 Mar 2010 11:57:15 -0700	[thread overview]
Message-ID: <adask7giak4.fsf@roland-alpha.cisco.com> (raw)
In-Reply-To: <u2ze2e108261003311136l4bcf1627n9ba4d3414167eef3-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org> (Bart Van Assche's message of "Wed, 31 Mar 2010 20:36:12 +0200")

 > Processing the flag IB_CQ_REPORT_MISSED_EVENTS causes several IB
 > drivers to lock and unlock a spinlock. Full-speed SRP I/O can cause
 > this operation to be invoked more than 100.000 times a second, so the
 > flag IB_CQ_REPORT_MISSED_EVENTS will have a small but measurable
 > impact on SRP I/O performance.

It seems the only driver where that happens is ehca.  But on the other
hand, for mthca/mlx4 it avoids doing something like:

  cq event:
    request notify <-- CQ is not empty, another event queued
    drain CQ

  cq event:
    request notify
    drain already empty CQ

ie the overhead saved here looks a lot more.
-- 
Roland Dreier <rolandd-FYB4Gu1CFyUAvxtiuMwx3w@public.gmane.org> || For corporate legal information go to:
http://www.cisco.com/web/about/doing_business/legal/cri/index.html
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  parent reply	other threads:[~2010-03-31 18:57 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2010-03-31 17:57 [PATCH 0/3] best practice for setting IB_CQ_REPORT_MISSED_EVENTS Ralph Campbell
     [not found] ` <20100331175742.24522.17850.stgit-/vjeY7uYZjrPXfVEPVhPGq6RkeBMCJyt@public.gmane.org>
2010-03-31 17:57   ` [PATCH 1/3] IB/core: use IB_CQ_REPORT_MISSED_EVENTS to avoid missed CQ callbacks Ralph Campbell
     [not found]     ` <20100331175747.24522.88472.stgit-/vjeY7uYZjrPXfVEPVhPGq6RkeBMCJyt@public.gmane.org>
2010-03-31 18:07       ` Sean Hefty
2010-03-31 18:17       ` Roland Dreier
     [not found]         ` <ada4ojwjqz7.fsf-BjVyx320WGW9gfZ95n9DRSW4+XlvGpQz@public.gmane.org>
2010-03-31 19:20           ` Ralph Campbell
     [not found]             ` <1270063245.4192.299.camel-/vjeY7uYZjrPXfVEPVhPGq6RkeBMCJyt@public.gmane.org>
2010-04-01  0:12               ` Roland Dreier
     [not found]                 ` <ada4ojwghey.fsf-BjVyx320WGW9gfZ95n9DRSW4+XlvGpQz@public.gmane.org>
2010-04-02 19:54                   ` Andy Grover
2010-03-31 17:57   ` [PATCH 2/3] IB/srp: " Ralph Campbell
     [not found]     ` <20100331175752.24522.66519.stgit-/vjeY7uYZjrPXfVEPVhPGq6RkeBMCJyt@public.gmane.org>
2010-03-31 18:11       ` Bart Van Assche
     [not found]         ` <y2ie2e108261003311111uec1ec00g746ba0ffe3d98799-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2010-03-31 18:18           ` Roland Dreier
     [not found]             ` <adazl1oiccb.fsf-BjVyx320WGW9gfZ95n9DRSW4+XlvGpQz@public.gmane.org>
2010-03-31 18:36               ` Bart Van Assche
     [not found]                 ` <u2ze2e108261003311136l4bcf1627n9ba4d3414167eef3-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2010-03-31 18:57                   ` Roland Dreier [this message]
     [not found]                     ` <adask7giak4.fsf-BjVyx320WGW9gfZ95n9DRSW4+XlvGpQz@public.gmane.org>
2010-03-31 19:16                       ` Bart Van Assche
2010-03-31 17:57   ` [PATCH 3/3] IB/iser: " Ralph Campbell

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