linux-kernel - [PATCH 1/2] null_blk: prevent timer handler running on a different CPU where started

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Message-Id: <1433201710-4284-1-git-send-email-akinobu.mita@gmail.com>
Date:	Tue,  2 Jun 2015 08:35:09 +0900
From:	Akinobu Mita <akinobu.mita@...il.com>
To:	linux-kernel@...r.kernel.org
Cc:	Akinobu Mita <akinobu.mita@...il.com>, Jens Axboe <axboe@...com>
Subject: [PATCH 1/2] null_blk: prevent timer handler running on a different CPU where started

When irqmode=2 (IRQ completion handler is timer), timer handler should
be called on the same CPU where the timer has been started.

Since completion_queues are per-cpu and the completion handler only
touches completion_queue for local CPU, we need to prevent the handler
from running on a different CPU where the timer has been started.
Otherwise, the IO cannot be completed until another completion handler
is executed on that CPU.

Signed-off-by: Akinobu Mita <akinobu.mita@...il.com>
Cc: Jens Axboe <axboe@...com>
---
 drivers/block/null_blk.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/block/null_blk.c b/drivers/block/null_blk.c
index 65cd61a..6f0a58e 100644
--- a/drivers/block/null_blk.c
+++ b/drivers/block/null_blk.c
@@ -257,7 +257,7 @@ static void null_cmd_end_timer(struct nullb_cmd *cmd)
 	if (llist_add(&cmd->ll_list, &cq->list)) {
 		ktime_t kt = ktime_set(0, completion_nsec);
 
-		hrtimer_start(&cq->timer, kt, HRTIMER_MODE_REL);
+		hrtimer_start(&cq->timer, kt, HRTIMER_MODE_REL_PINNED);
 	}
 
 	put_cpu();
-- 
1.9.1

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