linux-kernel - Re: [PATCH 2/2] scsi: register sysfs for scsi/iscsi workqueues

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Date:   Tue, 23 Jun 2020 12:44:31 +0200
From:   Benjamin Block <bblock@...ux.ibm.com>
To:     Mike Christie <michael.christie@...cle.com>
Cc:     Bob Liu <bob.liu@...cle.com>, linux-kernel@...r.kernel.org,
        tj@...nel.org, martin.petersen@...cle.com,
        linux-scsi@...r.kernel.org, open-iscsi@...glegroups.com,
        lduncan@...e.com, maier@...ux.ibm.com
Subject: Re: [PATCH 2/2] scsi: register sysfs for scsi/iscsi workqueues

On Mon, Jun 22, 2020 at 10:40:09AM -0500, Mike Christie wrote:
> On 6/11/20 5:07 AM, Bob Liu wrote:
> > This patch enable setting cpu affinity through "cpumask" for below
> > scsi/iscsi workqueues, so as to get better isolation.
> > - scsi_wq_*
> > - scsi_tmf_*
> > - iscsi_q_xx
> > - iscsi_eh
> > 
> > Signed-off-by: Bob Liu <bob.liu@...cle.com>
> > ---
> >   drivers/scsi/hosts.c                | 4 ++--
> >   drivers/scsi/libiscsi.c             | 2 +-
> >   drivers/scsi/scsi_transport_iscsi.c | 2 +-
> >   3 files changed, 4 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/scsi/hosts.c b/drivers/scsi/hosts.c
> > index 1d669e4..4b9f80d 100644
> > --- a/drivers/scsi/hosts.c
> > +++ b/drivers/scsi/hosts.c
> > @@ -272,7 +272,7 @@ int scsi_add_host_with_dma(struct Scsi_Host *shost, struct device *dev,
> >   	if (shost->transportt->create_work_queue) {
> >   		snprintf(shost->work_q_name, sizeof(shost->work_q_name),
> >   			 "scsi_wq_%d", shost->host_no);
> > -		shost->work_q = create_singlethread_workqueue(
> > +		shost->work_q = create_singlethread_workqueue_noorder(
> >   					shost->work_q_name);
> >   		if (!shost->work_q) {
> >   			error = -EINVAL;
> 
> This patch seems ok for the iscsi, fc, tmf, and non transport class scan
> uses. We are either heavy handed with flushes or did not need ordering.
> 
> I don't know about the zfcp use though, so I cc'd  the developers listed as
> maintainers. It looks like for zfcp we can do:

Thx for the notice.

> 
> zfcp_scsi_rport_register->fc_remote_port_add->fc_remote_port_create->scsi_queue_work
> to scan the scsi target on the rport.
> 
> and then zfcp_scsi_rport_register can call zfcp_unit_queue_scsi_scan->
> scsi_queue_work which will scan for a specific lun.
> 
> It looks ok if those are not ordered, but I would get their review to make
> sure.

I am not aware of any temporal requirements of those LUN-scans, so I
think making them not explicitly ordered shouldn't hurt us.

The target scan itself is protected again by `shost->scan_mutex`.. so
all fine I think.

-- 
Best Regards, Benjamin Block  / Linux on IBM Z Kernel Development / IBM Systems
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