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
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;
> }
> --
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