Patchwork [v3,1/3] block: add a non-queueable flush flag

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Submitter Shaohua Li
Date May 5, 2011, 1:59 a.m.
Message ID <20110505020417.586891398@sli10-conroe.sh.intel.com>
Download mbox | patch
Permalink /patch/94194/
State Not Applicable
Delegated to: David Miller
Headers show

Comments

Shaohua Li - May 5, 2011, 1:59 a.m.
flush request isn't queueable in some drives. Add a flag to let driver
notify block layer about this. We can optimize flush performance with the
knowledge.

Signed-off-by: Shaohua Li <shaohua.li@intel.com>
---
 block/blk-settings.c   |    6 ++++++
 include/linux/blkdev.h |    7 +++++++
 2 files changed, 13 insertions(+)


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Jeff Garzik - May 5, 2011, 2:17 a.m.
On 05/04/2011 09:59 PM, shaohua.li@intel.com wrote:
> flush request isn't queueable in some drives. Add a flag to let driver
> notify block layer about this. We can optimize flush performance with the
> knowledge.
>
> Signed-off-by: Shaohua Li<shaohua.li@intel.com>
> ---
>   block/blk-settings.c   |    6 ++++++
>   include/linux/blkdev.h |    7 +++++++
>   2 files changed, 13 insertions(+)

hmmm.

This assumes that flush on new hardware, by default, is queueable.

I think the sense should be reversed:  don't enable the optimization, 
unless we know the optimization works.

That seems safer than always enabling the optimization, unless we know 
it does not work.  That is not a fail-safe mode of operation.

	Jeff




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Shaohua Li - May 5, 2011, 2:21 a.m.
On Thu, May 05, 2011 at 10:17:39AM +0800, Jeff Garzik wrote:
> On 05/04/2011 09:59 PM, shaohua.li@intel.com wrote:
> > flush request isn't queueable in some drives. Add a flag to let driver
> > notify block layer about this. We can optimize flush performance with the
> > knowledge.
> >
> > Signed-off-by: Shaohua Li<shaohua.li@intel.com>
> > ---
> >   block/blk-settings.c   |    6 ++++++
> >   include/linux/blkdev.h |    7 +++++++
> >   2 files changed, 13 insertions(+)
> 
> hmmm.
> 
> This assumes that flush on new hardware, by default, is queueable.
> 
> I think the sense should be reversed:  don't enable the optimization, 
> unless we know the optimization works.
> 
> That seems safer than always enabling the optimization, unless we know 
> it does not work.  That is not a fail-safe mode of operation.
This assumes flush is queueable by default. but I only enable the optimization
for non-queueable flush. So the optimization is off by default, please see
the second patch.

Thanks,
Shaohua
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Tejun Heo - May 5, 2011, 7:53 a.m.
On Thu, May 05, 2011 at 09:59:33AM +0800, shaohua.li@intel.com wrote:
> flush request isn't queueable in some drives. Add a flag to let driver
> notify block layer about this. We can optimize flush performance with the
> knowledge.
> 
> Signed-off-by: Shaohua Li <shaohua.li@intel.com>

Acked-by: Tejun Heo <tj@kernel.org>

Thanks.

Patch

Index: linux/include/linux/blkdev.h
===================================================================
--- linux.orig/include/linux/blkdev.h	2011-05-04 14:23:42.000000000 +0800
+++ linux/include/linux/blkdev.h	2011-05-05 09:05:18.000000000 +0800
@@ -364,6 +364,7 @@  struct request_queue
 	 * for flush operations
 	 */
 	unsigned int		flush_flags;
+	unsigned int		flush_not_queueable:1;
 	unsigned int		flush_pending_idx:1;
 	unsigned int		flush_running_idx:1;
 	unsigned long		flush_pending_since;
@@ -843,6 +844,7 @@  extern void blk_queue_softirq_done(struc
 extern void blk_queue_rq_timed_out(struct request_queue *, rq_timed_out_fn *);
 extern void blk_queue_rq_timeout(struct request_queue *, unsigned int);
 extern void blk_queue_flush(struct request_queue *q, unsigned int flush);
+extern void blk_queue_flush_queueable(struct request_queue *q, bool queueable);
 extern struct backing_dev_info *blk_get_backing_dev_info(struct block_device *bdev);
 
 extern int blk_rq_map_sg(struct request_queue *, struct request *, struct scatterlist *);
@@ -1111,6 +1113,11 @@  static inline unsigned int block_size(st
 	return bdev->bd_block_size;
 }
 
+static inline bool queue_flush_queueable(struct request_queue *q)
+{
+	return !q->flush_not_queueable;
+}
+
 typedef struct {struct page *v;} Sector;
 
 unsigned char *read_dev_sector(struct block_device *, sector_t, Sector *);
Index: linux/block/blk-settings.c
===================================================================
--- linux.orig/block/blk-settings.c	2011-05-05 08:37:05.000000000 +0800
+++ linux/block/blk-settings.c	2011-05-05 09:02:16.000000000 +0800
@@ -790,6 +790,12 @@  void blk_queue_flush(struct request_queu
 }
 EXPORT_SYMBOL_GPL(blk_queue_flush);
 
+void blk_queue_flush_queueable(struct request_queue *q, bool queueable)
+{
+	q->flush_not_queueable = !queueable;
+}
+EXPORT_SYMBOL_GPL(blk_queue_flush_queueable);
+
 static int __init blk_settings_init(void)
 {
 	blk_max_low_pfn = max_low_pfn - 1;