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[PATCH] block: Make rq_affinity = 1 work as expected

To: linux-fsdevel@xxxxxxxxxxxxxxx
Subject: [PATCH] block: Make rq_affinity = 1 work as expected
From: Jan Kara <jack@xxxxxxx>
Date: Fri, 10 Oct 2014 16:23:09 +0200
Cc: linux-ext4@xxxxxxxxxxxxxxx, Dave Chinner <david@xxxxxxxxxxxxx>, xfs@xxxxxxxxxxx, cluster-devel@xxxxxxxxxx, Steven Whitehouse <swhiteho@xxxxxxxxxx>, Mark Fasheh <mfasheh@xxxxxxxx>, Joel Becker <jlbec@xxxxxxxxxxxx>, ocfs2-devel@xxxxxxxxxxxxxx, reiserfs-devel@xxxxxxxxxxxxxxx, Jeff Mahoney <jeffm@xxxxxxx>, Dave Kleikamp <shaggy@xxxxxxxxxx>, jfs-discussion@xxxxxxxxxxxxxxxxxxxxx, tytso@xxxxxxx, viro@xxxxxxxxxxxxxxxxxx, Tao Ma <boyu.mt@xxxxxxxxxx>, Christoph Hellwig <hch@xxxxxxxxxxxxx>, Roland Dreier <roland@xxxxxxxxxxxxxxx>, Dan Williams <dan.j.williams@xxxxxxxxx>, Jens Axboe <jaxboe@xxxxxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <1412951028-4085-1-git-send-email-jack@xxxxxxx>
References: <1412951028-4085-1-git-send-email-jack@xxxxxxx>
From: Tao Ma <boyu.mt@xxxxxxxxxx>

Commit 5757a6d76c introduced a new rq_affinity = 2 so as to make
the request completed in the __make_request cpu. But it makes the
old rq_affinity = 1 not work any more. The root cause is that
if the 'cpu' and 'req->cpu' is in the same group and cpu != req->cpu,
ccpu will be the same as group_cpu, so the completion will be
excuted in the 'cpu' not 'group_cpu'.

This patch fix problem by simpling removing group_cpu and the codes
are more explicit now. If ccpu == cpu, we complete in cpu, otherwise
we raise_blk_irq to ccpu.

Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Cc: Roland Dreier <roland@xxxxxxxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Jens Axboe <jaxboe@xxxxxxxxxxxx>
Signed-off-by: Tao Ma <boyu.mt@xxxxxxxxxx>
Reviewed-by: Shaohua Li <shaohua.li@xxxxxxxxx>
Signed-off-by: Jens Axboe <jaxboe@xxxxxxxxxxxx>
---
 block/blk-softirq.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/block/blk-softirq.c b/block/blk-softirq.c
index 475fab809a80..487addc85bb5 100644
--- a/block/blk-softirq.c
+++ b/block/blk-softirq.c
@@ -103,7 +103,7 @@ static struct notifier_block __cpuinitdata blk_cpu_notifier 
= {
 
 void __blk_complete_request(struct request *req)
 {
-       int ccpu, cpu, group_cpu = NR_CPUS;
+       int ccpu, cpu;
        struct request_queue *q = req->q;
        unsigned long flags;
 
@@ -117,14 +117,12 @@ void __blk_complete_request(struct request *req)
         */
        if (test_bit(QUEUE_FLAG_SAME_COMP, &q->queue_flags) && req->cpu != -1) {
                ccpu = req->cpu;
-               if (!test_bit(QUEUE_FLAG_SAME_FORCE, &q->queue_flags)) {
+               if (!test_bit(QUEUE_FLAG_SAME_FORCE, &q->queue_flags))
                        ccpu = blk_cpu_to_group(ccpu);
-                       group_cpu = blk_cpu_to_group(cpu);
-               }
        } else
                ccpu = cpu;
 
-       if (ccpu == cpu || ccpu == group_cpu) {
+       if (ccpu == cpu) {
                struct list_head *list;
 do_local:
                list = &__get_cpu_var(blk_cpu_done);
-- 
1.8.1.4

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