From: Ming Lei <ming.lei@canonical.com>
Date: Sun, 6 Jul 2014 14:39:26 +0000 (+0200)
Subject: virtio-scsi: replace target spinlock with seqcount
X-Git-Tag: omap-for-v3.17/fixes-against-rc2~143^2~36
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=938ece711c5b1ba4fa8e3b9fc8cc03843ae82a5b;p=pandora-kernel.git

virtio-scsi: replace target spinlock with seqcount

The spinlock of tgt_lock is only for serializing read and write
req_vq, one lockless seqcount is enough for the purpose.

On one 16core VM with vhost-scsi backend, the patch can improve
IOPS with 3% on random read test.

Signed-off-by: Ming Lei <ming.lei@canonical.com>
[Add initialization in virtscsi_target_alloc. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
---

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