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Date:   Fri, 1 May 2020 19:45:05 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Ming Lei <ming.lei@redhat.com>
Cc:     Hannes Reinecke <hare@suse.de>,
        "Martin K. Petersen" <martin.petersen@oracle.com>,
        Christoph Hellwig <hch@lst.de>,
        James Bottomley <james.bottomley@hansenpartnership.com>,
        John Garry <john.garry@huawei.com>,
        Bart van Assche <bvanassche@acm.org>,
        linux-scsi@vger.kernel.org, Hannes Reinecke <hare@suse.com>
Subject: Re: [PATCH RFC v3 04/41] csiostor: use reserved command for LUN
 reset
Message-ID: <20200501174505.GC23795@lst.de>
References: <20200430131904.5847-1-hare@suse.de> <20200430131904.5847-5-hare@suse.de> <20200430151546.GB1005453@T590> <cd0f88db-96ec-d69f-f33e-b10a1cb3756d@suse.de> <20200501150129.GB1012188@T590>
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On Fri, May 01, 2020 at 11:01:29PM +0800, Ming Lei wrote:
> > We cannot increase MAX_QUEUE arbitrarily as this is a compile time variable,
> > which seems to relate to a hardware setting.
> > 
> > But I can see to update the reserved command functionality for allowing to
> > fetch commands from the normal I/O tag pool; in the case of LUN reset it
> > shouldn't make much of a difference as the all I/O is quiesced anyway.
> 
> It isn't related with reset.
> 
> This patch reduces active IO queue depth by 1 anytime no matter there is reset
> or not, and this way may cause performance regression.

But isn't it the right thing to do?  How else do we guarantee that
there always is a tag available for the LU reset?