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authorChristoph Hellwig <hch@lst.de>2014-01-17 12:06:53 +0100
committerChristoph Hellwig <hch@lst.de>2014-07-25 17:16:28 -0400
commitd285203cf647d7c97db3a1c33794315c9008593f (patch)
treea28a0a902cf3f467e326a02f5632b917b75c56a3 /drivers/scsi/hosts.c
parentc53c6d6a68b13b1dff2892551b56cfdc07887d9e (diff)
downloadlinux-d285203cf647d7c97db3a1c33794315c9008593f.tar.bz2
scsi: add support for a blk-mq based I/O path.
This patch adds support for an alternate I/O path in the scsi midlayer which uses the blk-mq infrastructure instead of the legacy request code. Use of blk-mq is fully transparent to drivers, although for now a host template field is provided to opt out of blk-mq usage in case any unforseen incompatibilities arise. In general replacing the legacy request code with blk-mq is a simple and mostly mechanical transformation. The biggest exception is the new code that deals with the fact the I/O submissions in blk-mq must happen from process context, which slightly complicates the I/O completion handler. The second biggest differences is that blk-mq is build around the concept of preallocated requests that also include driver specific data, which in SCSI context means the scsi_cmnd structure. This completely avoids dynamic memory allocations for the fast path through I/O submission. Due the preallocated requests the MQ code path exclusively uses the host-wide shared tag allocator instead of a per-LUN one. This only affects drivers actually using the block layer provided tag allocator instead of their own. Unlike the old path blk-mq always provides a tag, although drivers don't have to use it. For now the blk-mq path is disable by defauly and must be enabled using the "use_blk_mq" module parameter. Once the remaining work in the block layer to make blk-mq more suitable for slow devices is complete I hope to make it the default and eventually even remove the old code path. Based on the earlier scsi-mq prototype by Nicholas Bellinger. Thanks to Bart Van Assche and Robert Elliot for testing, benchmarking and various sugestions and code contributions. Signed-off-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com> Reviewed-by: Hannes Reinecke <hare@suse.de> Reviewed-by: Webb Scales <webbnh@hp.com> Acked-by: Jens Axboe <axboe@kernel.dk> Tested-by: Bart Van Assche <bvanassche@acm.org> Tested-by: Robert Elliott <elliott@hp.com>
Diffstat (limited to 'drivers/scsi/hosts.c')
-rw-r--r--drivers/scsi/hosts.c35
1 files changed, 30 insertions, 5 deletions
diff --git a/drivers/scsi/hosts.c b/drivers/scsi/hosts.c
index 0632eee82620..6de80e352871 100644
--- a/drivers/scsi/hosts.c
+++ b/drivers/scsi/hosts.c
@@ -213,9 +213,24 @@ int scsi_add_host_with_dma(struct Scsi_Host *shost, struct device *dev,
goto fail;
}
+ if (shost_use_blk_mq(shost)) {
+ error = scsi_mq_setup_tags(shost);
+ if (error)
+ goto fail;
+ }
+
+ /*
+ * Note that we allocate the freelist even for the MQ case for now,
+ * as we need a command set aside for scsi_reset_provider. Having
+ * the full host freelist and one command available for that is a
+ * little heavy-handed, but avoids introducing a special allocator
+ * just for this. Eventually the structure of scsi_reset_provider
+ * will need a major overhaul.
+ */
error = scsi_setup_command_freelist(shost);
if (error)
- goto fail;
+ goto out_destroy_tags;
+
if (!shost->shost_gendev.parent)
shost->shost_gendev.parent = dev ? dev : &platform_bus;
@@ -226,7 +241,7 @@ int scsi_add_host_with_dma(struct Scsi_Host *shost, struct device *dev,
error = device_add(&shost->shost_gendev);
if (error)
- goto out;
+ goto out_destroy_freelist;
pm_runtime_set_active(&shost->shost_gendev);
pm_runtime_enable(&shost->shost_gendev);
@@ -279,8 +294,11 @@ int scsi_add_host_with_dma(struct Scsi_Host *shost, struct device *dev,
device_del(&shost->shost_dev);
out_del_gendev:
device_del(&shost->shost_gendev);
- out:
+ out_destroy_freelist:
scsi_destroy_command_freelist(shost);
+ out_destroy_tags:
+ if (shost_use_blk_mq(shost))
+ scsi_mq_destroy_tags(shost);
fail:
return error;
}
@@ -309,8 +327,13 @@ static void scsi_host_dev_release(struct device *dev)
}
scsi_destroy_command_freelist(shost);
- if (shost->bqt)
- blk_free_tags(shost->bqt);
+ if (shost_use_blk_mq(shost)) {
+ if (shost->tag_set.tags)
+ scsi_mq_destroy_tags(shost);
+ } else {
+ if (shost->bqt)
+ blk_free_tags(shost->bqt);
+ }
kfree(shost->shost_data);
@@ -436,6 +459,8 @@ struct Scsi_Host *scsi_host_alloc(struct scsi_host_template *sht, int privsize)
else
shost->dma_boundary = 0xffffffff;
+ shost->use_blk_mq = scsi_use_blk_mq && !shost->hostt->disable_blk_mq;
+
device_initialize(&shost->shost_gendev);
dev_set_name(&shost->shost_gendev, "host%d", shost->host_no);
shost->shost_gendev.bus = &scsi_bus_type;