From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Return-Path: Message-ID: <1524844550.30534.1.camel@redhat.com> Subject: Re: [PATCH 0/3] scsi: scsi-mq: don't hold host_busy in IO path From: Laurence Oberman To: Bart Van Assche , "axboe@kernel.dk" , "ming.lei@redhat.com" Cc: "linux-block@vger.kernel.org" , "snitzer@redhat.com" , "hch@lst.de" , "martin.petersen@oracle.com" , "hare@suse.de" , "linux-scsi@vger.kernel.org" , "don.brace@microsemi.com" , "james.bottomley@hansenpartnership.com" , "osandov@fb.com" , "kashyap.desai@broadcom.com" Date: Fri, 27 Apr 2018 11:55:50 -0400 In-Reply-To: <647b4fe833fdf001f724cfa0803c9e3a79d78b13.camel@wdc.com> References: <20180420065742.8043-1-ming.lei@redhat.com> <87619135ac0bfefa07f510170024b609e641db0c.camel@wdc.com> <607c4d2f-28e7-4152-dbf5-7fb4387e9413@kernel.dk> <647b4fe833fdf001f724cfa0803c9e3a79d78b13.camel@wdc.com> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 List-ID: On Fri, 2018-04-27 at 15:48 +0000, Bart Van Assche wrote: > On Fri, 2018-04-27 at 09:39 -0600, Jens Axboe wrote: > > blk_mq_tagset_busy_iter(&shost->tag_set, scsi_host_check_in_flight, > > &in_flight); > > return in_flight.cnt + atomic_read(&shost->host_busy); > > > > The atomic read is basically free, once we get rid of the dirty of > > that > > variable on each IO. > > Hello Jens, > > What makes you think that " + atomic_read(&shost->host_busy)" is > necessary? > I am not aware of any code outside the SCSI core that modifies the > host_busy > member. > > Thanks, > > Bart. > > > As part of testing latest upstream in MQ and non-MQ I intend to test this patch series fully on actual hardware F/C 8G to memory backed array LUNS and of course SRP/RDMA I have started working on this and will report back. Thanks Laurence