On Mon, Mar 28, 2016 at 4:53 PM, Mike Christie <mchristi@xxxxxxxxxx> wrote:
> On 03/28/2016 03:46 PM, Richard Sharpe wrote:
>> Hi folks,
>>
>> We noticed recently while testing with large numbers of iSCSI
>> connections that iscsid was going to heroic lengths to change the nice
>> value of the iSCSI work queue to -20. It becomes very expensive with
>> hundreds of connections.
>>
>> This small patch has the LLD do the work,
>>
>> Feedback welcome.
>>
>> A small patch will be needed for the user-space tools as well. I will
>> send one in if someone else does not do so.
>>
>> -- Regards, Richard Sharpe (何以解憂？唯有杜康。--曹操)
>>
>>
>> 0001-Make-the-iscsi-lld-create-a-WQ_HIGHPRI-workqueue.patch
>>
>>
>> From c0f04a66b29a9190109740c03ee9e65bb62afe28 Mon Sep 17 00:00:00 2001
>> From: Richard Sharpe <rsharpe@xxxxxxxxxxx>
>> Date: Mon, 28 Mar 2016 13:36:18 -0700
>> Subject: [PATCH] Make the iscsi lld create a WQ_HIGHPRI workqueue.
>>
>> The open-iscsi tools go to heroic efforts to change the nice value of
>> the iscsi workqueue to -20. It scans all processes in /proc and
>> when it finds the one it is interested in calls setpriority.
>>
>> When you are connecting to a reasonable number of iSCSI targets this
>> can be costly.
>>
>> This small patch has the iscsi LLD do the work itself. It seems like
>> the least intrusive way to acheive the result.
>>
>> A small patch will be needed in the open-iscsi userspace tools
>> as well.
>>
>> Signed-off-by: Richard Sharpe <realrichardsharpe@xxxxxxxxx>
>> ---
>> drivers/scsi/libiscsi.c | 4 +++-
>> 1 files changed, 3 insertions(+), 1 deletions(-)
>>
>> diff --git a/drivers/scsi/libiscsi.c b/drivers/scsi/libiscsi.c
>> index 6bffd91..abaefe1 100644
>> --- a/drivers/scsi/libiscsi.c
>> +++ b/drivers/scsi/libiscsi.c
>> @@ -2615,9 +2615,11 @@ struct Scsi_Host *iscsi_host_alloc(struct scsi_host_template *sht,
>> ihost = shost_priv(shost);
>>
>> if (xmit_can_sleep) {
>> + int wq_flags = __WQ_LEGACY | WQ_MEM_RECLAIM | WQ_HIGHPRI;
>
>
> I do not think we need to or are supposed to be setting __WQ_LEGACY. It
> looks like it was only to catch the case here
OK, I will fix that and resubmit.
> https://lkml.org/lkml/2016/1/29/179
>
>
>
>> snprintf(ihost->workq_name, sizeof(ihost->workq_name),
>> "iscsi_q_%d", shost->host_no);
>> - ihost->workq = create_singlethread_workqueue(ihost->workq_name);
>> + ihost->workq = alloc_ordered_workqueue("%s", wq_flags,
>> + ihost->workq_name);
>> if (!ihost->workq)
>> goto free_host;
>> }
>> --
>
--
Regards,
Richard Sharpe
(何以解憂？唯有杜康。--曹操)
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