Re: [PATCH 3/4] tcm_vhost: Fix vs->vs_endpoint checking in vhost_scsi_handle_vq()

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Il 13/03/2013 04:13, Asias He ha scritto:
>> > This takes dev mutex on data path which will introduce
>> > contention esp for multiqueue.
> Yes, for now it is okay, but for concurrent execution of multiqueue it is
> really bad.
> 
> By the way, what is the overhead of taking and releasing the
> vs->dev.mutex even if no one contents for it? Is this overhead gnorable.

There is a possibility of cacheline ping-pong, but apart from that it's
ignorable.

>> > How about storing the endpoint as part of vq
>> > private data and protecting with vq mutex?
> 
> Hmm, this makes sense, let's see how well it works.

Then VHOST_SCSI_SET_ENDPOINT would have to go through all vqs, no?  A
rwlock seems simpler.

Paolo
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