diff options
| author | Tim Chase <[email protected]> | 2016-07-08 10:33:01 -0500 |
|---|---|---|
| committer | Brian Behlendorf <[email protected]> | 2016-07-25 14:24:47 -0700 |
| commit | e6603b7c1fc7ac01f8891b11df34d943812153e9 (patch) | |
| tree | 9fede819ea53702b3be37ee0a5600c7c862915be /config | |
| parent | 273ff9b5ccc438e3099809c43229cc75503cff68 (diff) | |
Fix sync behavior for disk vdevs
Prior to b39c22b, which was first generally available in the 0.6.5
release as b39c22b, ZoL never actually submitted synchronous read or write
requests to the Linux block layer. This means the vdev_disk_dio_is_sync()
function had always returned false and, therefore, the completion in
dio_request_t.dr_comp was never actually used.
In b39c22b, synchronous ZIO operations were translated to synchronous
BIO requests in vdev_disk_io_start(). The follow-on commits 5592404 and
aa159af fixed several problems introduced by b39c22b. In particular,
5592404 introduced the new flag parameter "wait" to __vdev_disk_physio()
but under ZoL, since vdev_disk_physio() is never actually used, the wait
flag was always zero so the new code had no effect other than to cause
a bug in the use of the dio_request_t.dr_comp which was fixed by aa159af.
The original rationale for introducing synchronous operations in b39c22b
was to hurry certains requests through the BIO layer which would have
otherwise been subject to its unplug timer which would increase the
latency. This behavior of the unplug timer, however, went away during the
transition of the plug/unplug system between kernels 2.6.32 and 2.6.39.
To handle the unplug timer behavior on 2.6.32-2.6.35 kernels the
BIO_RW_UNPLUG flag is used as a hint to suppress the plugging behavior.
For kernels 2.6.36-2.6.38, the REQ_UNPLUG macro will be available and
ise used for the same purpose.
Signed-off-by: Tim Chase <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>
Closes #4858
Diffstat (limited to 'config')
| -rw-r--r-- | config/kernel-blk-queue-unplug.m4 | 23 | ||||
| -rw-r--r-- | config/kernel.m4 | 1 |
2 files changed, 24 insertions, 0 deletions
diff --git a/config/kernel-blk-queue-unplug.m4 b/config/kernel-blk-queue-unplug.m4 new file mode 100644 index 000000000..45cc2322a --- /dev/null +++ b/config/kernel-blk-queue-unplug.m4 @@ -0,0 +1,23 @@ +dnl # +dnl # 2.6.32-2.6.35 API - The BIO_RW_UNPLUG enum can be used as a hint +dnl # to unplug the queue. +dnl # +AC_DEFUN([ZFS_AC_KERNEL_BLK_QUEUE_HAVE_BIO_RW_UNPLUG], [ + AC_MSG_CHECKING([whether the BIO_RW_UNPLUG enum is available]) + tmp_flags="$EXTRA_KCFLAGS" + EXTRA_KCFLAGS="${NO_UNUSED_BUT_SET_VARIABLE}" + ZFS_LINUX_TRY_COMPILE([ + #include <linux/blkdev.h> + ],[ + extern enum bio_rw_flags rw; + + rw = BIO_RW_UNPLUG; + ],[ + AC_MSG_RESULT(yes) + AC_DEFINE(HAVE_BLK_QUEUE_HAVE_BIO_RW_UNPLUG, 1, + [BIO_RW_UNPLUG is available]) + ],[ + AC_MSG_RESULT(no) + ]) + EXTRA_KCFLAGS="$tmp_flags" +]) diff --git a/config/kernel.m4 b/config/kernel.m4 index c9b24cbe8..ac6c08ffe 100644 --- a/config/kernel.m4 +++ b/config/kernel.m4 @@ -27,6 +27,7 @@ AC_DEFUN([ZFS_AC_CONFIG_KERNEL], [ ZFS_AC_KERNEL_BLK_QUEUE_FLUSH ZFS_AC_KERNEL_BLK_QUEUE_MAX_HW_SECTORS ZFS_AC_KERNEL_BLK_QUEUE_MAX_SEGMENTS + ZFS_AC_KERNEL_BLK_QUEUE_HAVE_BIO_RW_UNPLUG ZFS_AC_KERNEL_GET_DISK_RO ZFS_AC_KERNEL_GET_GENDISK ZFS_AC_KERNEL_DISCARD_GRANULARITY |