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From: Flavio Baronti <f.baronti-ngIpsMLAhaq41k5uCYKmRQ@public.gmane.org>
To: "linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org"
	<linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>
Subject: ibv_req_notify_cq and multithreading
Date: Thu, 12 Jan 2012 12:34:58 +0100	[thread overview]
Message-ID: <4F0EC562.2040709@list-group.com> (raw)

I'm trying to have N threads reading from the same completion channel, bounded to M completion queues. I would like to 
have N << M, and to ensure that only a single thread at time can call ibv_poll_cq() on a given queue, to process the 
events in the same order they were put in the queue.

I can't understand how to properly achieve this, since:
1- If I call ibv_req_notify_cq() before ibv_poll_cq(), I might end up with two threads polling the same queue.
2- If I call ibv_req_notify_cq() after ibv_poll_cq(), I could end up with events in the cq not being notified in the 
channel (I read this on the IBTA 11.4.2.2, and I *think* I actually experienced this under load).

I can use option 1 with an additional lock before ibv_req_notify_cq(), but I would like to know if there is a simpler 
way which I can't see.

Thanks
Flavio
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             reply	other threads:[~2012-01-12 11:34 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-01-12 11:34 Flavio Baronti [this message]
     [not found] ` <4F0EC562.2040709-ngIpsMLAhaq41k5uCYKmRQ@public.gmane.org>
2012-01-12 15:52   ` ibv_req_notify_cq and multithreading Hefty, Sean
     [not found]     ` <1828884A29C6694DAF28B7E6B8A8237325676B8F-P5GAC/sN6hmkrb+BlOpmy7fspsVTdybXVpNB7YpNyf8@public.gmane.org>
2012-01-13  8:10       ` Flavio Baronti
     [not found]         ` <4F0FE6D9.4050403-ngIpsMLAhaq41k5uCYKmRQ@public.gmane.org>
2012-01-13 16:37           ` Hefty, Sean

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