linux-kernel - Re: [lustre-devel] [PATCH 08/16] staging: lustre: open code polling loop instead of using l_wait

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Date:   Mon, 18 Dec 2017 20:55:10 +0000
From:   Patrick Farrell <paf@...y.com>
To:     NeilBrown <neilb@...e.com>, Oleg Drokin <oleg.drokin@...el.com>,
        "Andreas Dilger" <andreas.dilger@...el.com>,
        James Simmons <jsimmons@...radead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:     lkml <linux-kernel@...r.kernel.org>,
        lustre <lustre-devel@...ts.lustre.org>
Subject: Re: [lustre-devel] [PATCH 08/16] staging: lustre: open code polling
 loop instead of using l_wait_event()

The lov_check_and_wait_active wait is usually (always?) going to be
asynchronous from userspace and probably shouldn¹t contribute to load.

So I guess that means schedule_timeout_idle.

On 12/18/17, 1:18 AM, "lustre-devel on behalf of NeilBrown"
<lustre-devel-bounces@...ts.lustre.org on behalf of neilb@...e.com> wrote:

>Two places that LWI_TIMEOUT_INTERVAL() is used, the outcome is a
>simple polling loop that polls every second for some event (with a
>limit).
>
>So write a simple loop to make this more apparent.
>
>Signed-off-by: NeilBrown <neilb@...e.com>
>---
> drivers/staging/lustre/lustre/llite/llite_lib.c |   11 +++++------
> drivers/staging/lustre/lustre/lov/lov_request.c |   12 +++++-------
> 2 files changed, 10 insertions(+), 13 deletions(-)
>
>diff --git a/drivers/staging/lustre/lustre/llite/llite_lib.c
>b/drivers/staging/lustre/lustre/llite/llite_lib.c
>index 33dc15e9aebb..f6642fa30428 100644
>--- a/drivers/staging/lustre/lustre/llite/llite_lib.c
>+++ b/drivers/staging/lustre/lustre/llite/llite_lib.c
>@@ -1984,8 +1984,7 @@ void ll_umount_begin(struct super_block *sb)
> 	struct ll_sb_info *sbi = ll_s2sbi(sb);
> 	struct obd_device *obd;
> 	struct obd_ioctl_data *ioc_data;
>-	wait_queue_head_t waitq;
>-	struct l_wait_info lwi;
>+	int cnt = 0;
> 
> 	CDEBUG(D_VFSTRACE, "VFS Op: superblock %p count %d active %d\n", sb,
> 	       sb->s_count, atomic_read(&sb->s_active));
>@@ -2021,10 +2020,10 @@ void ll_umount_begin(struct super_block *sb)
> 	 * and then continue. For now, we just periodically checking for vfs
> 	 * to decrement mnt_cnt and hope to finish it within 10sec.
> 	 */
>-	init_waitqueue_head(&waitq);
>-	lwi = LWI_TIMEOUT_INTERVAL(10 * HZ,
>-				   HZ, NULL, NULL);
>-	l_wait_event(waitq, may_umount(sbi->ll_mnt.mnt), &lwi);
>+	while (cnt < 10 && !may_umount(sbi->ll_mnt.mnt)) {
>+		schedule_timeout_uninterruptible(HZ);
>+		cnt ++;
>+	}
> 
> 	schedule();
> }
>diff --git a/drivers/staging/lustre/lustre/lov/lov_request.c
>b/drivers/staging/lustre/lustre/lov/lov_request.c
>index fb3b7a7fa32a..c1e58fcc30b3 100644
>--- a/drivers/staging/lustre/lustre/lov/lov_request.c
>+++ b/drivers/staging/lustre/lustre/lov/lov_request.c
>@@ -99,8 +99,7 @@ static int lov_check_set(struct lov_obd *lov, int idx)
>  */
> static int lov_check_and_wait_active(struct lov_obd *lov, int ost_idx)
> {
>-	wait_queue_head_t waitq;
>-	struct l_wait_info lwi;
>+	int cnt = 0;
> 	struct lov_tgt_desc *tgt;
> 	int rc = 0;
> 
>@@ -125,11 +124,10 @@ static int lov_check_and_wait_active(struct lov_obd
>*lov, int ost_idx)
> 
> 	mutex_unlock(&lov->lov_lock);
> 
>-	init_waitqueue_head(&waitq);
>-	lwi = LWI_TIMEOUT_INTERVAL(obd_timeout * HZ,
>-				   HZ, NULL, NULL);
>-
>-	rc = l_wait_event(waitq, lov_check_set(lov, ost_idx), &lwi);
>+	while (cnt < obd_timeout && !lov_check_set(lov, ost_idx)) {
>+		schedule_timeout_uninterruptible(HZ);
>+		cnt ++;
>+	}
> 	if (tgt->ltd_active)
> 		return 1;
> 
>
>
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