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Reinstate zvol_taskq to fix aio on zvol

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Commit 37f9dac removed the zvol_taskq for processing zvol requests.
This was removed as part of switching to make_request_fn and was
motivated by a concern at the time over dispatch latency.

However, this also made all bio request synchronous, and caused
serious performance issues as the bio submitter would wait for
every bio it submitted, effectively making the IO depth 1.

This patch reinstate zvol_taskq, and to make sure overlapped I/Os
are ordered properly, we take range lock in zvol_request, and pass
it along with bio to the I/O functions zvol_{write,discard,read}.

In order to facilitate benchmarks a zvol_request_sync module
option was added to switch between sync and async request handling.
For the moment, the default behavior is synchronous but this is
likely to change pending additional testing.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Chunwei Chen <david.chen@osnexus.com>
Closes #5824
This commit is contained in:
Chunwei Chen
2017-02-22 16:08:04 -08:00
committed by Brian Behlendorf
parent e815485fe9
commit 692e55b8fe
3 changed files with 201 additions and 84 deletions
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include/linux/blkdev_compat.h
+9 -2
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@@ -498,8 +498,15 @@ blk_queue_discard_granularity(struct request_queue *q, unsigned int dg)
#define VDEV_HOLDER ((void *)0x2401de7)
#ifndef HAVE_GENERIC_IO_ACCT
#define generic_start_io_acct(rw, slen, part) ((void)0)
#define generic_end_io_acct(rw, part, start_jiffies) ((void)0)
static inline void
generic_start_io_acct(int rw, unsigned long sectors, struct hd_struct *part)
{
}
static inline void
generic_end_io_acct(int rw, struct hd_struct *part, unsigned long start_time)
{
}
#endif
#endif /* _ZFS_BLKDEV_H */