Josh Paetzel 9a625bd31c MFV 316870 ... 7448 ZFS doesn't notice when disk vdevs have no write cache illumos/illumos-gate@295438ba32 295438ba32 https://www.illumos.org/issues/7448 I built a SmartOS image with all the NVMe commits including 7372 (support NVMe volatile write cache) and repeated my dd testing: > #!/bin/bash > for i in `seq 1 1000`; do > dd if=/dev/zero of=file00 bs=1M count=102400 oflag=sync & > dd if=/dev/zero of=file01 bs=1M count=102400 oflag=sync & > wait > rm file00 file01 > done > Previously each dd command took ~145 seconds to finish, now it takes ~400 seconds. Eventually I figured out it is 7372 that causes unnecessary nvme_bd_sync() executions which wasted CPU cycles. If a NVMe device doesn't support a write cache, the nvme_bd_sync function will return ENOTSUP to indicate this to upper layers. It seems this returned value is ignored by ZFS, and as such this bug is not really specific to NVMe. In vdev_disk_io_start() ZFS sends the flush to the disk driver (blkdev) with a callback to vdev_disk_ioctl_done(). As nvme filled in the bd_sync_cache function pointer, blkdev will not return ENOTSUP, as the nvme driver in general does support cache flush. Instead it will issue an asynchronous flush to nvme and immediately return 0, and hence ZFS will not set vdev_nowritecache here. The nvme driver will at some point process the cache flush command, and if there is no write cache on the device it will return ENOTSUP, which will be delivered to the vdev_disk_ioctl_done() callback. This function will not check the error code and not set nowritecache. The right place to check the error code from the cache flush is in zio_vdev_io_assess(). This would catch both cases, synchronous and asynchronous cache flushes. This would also be independent of the implementation detail that some drivers can return ENOTSUP immediately. Reviewed by: Dan Fields <dan.fields@nexenta.com> Reviewed by: Alek Pinchuk <alek.pinchuk@nexenta.com> Reviewed by: George Wilson <george.wilson@delphix.com> Approved by: Dan McDonald <danmcd@omniti.com> Author: Hans Rosenfeld <hans.rosenfeld@nexenta.com> Obtained from: Illumos		2017-04-21 00:17:54 +00:00
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ctf
dtrace	Use pget() instead of pfind() in fasttrap_pid_{enable,disable}().	2017-02-15 06:07:01 +00:00
fs	MFV 316870	2017-04-21 00:17:54 +00:00
os	Mechanically convert cddl sun #ifdef's to illumos	2015-01-17 14:44:59 +00:00
sys	zfs: clean up unused files and definitions	2017-02-24 07:53:56 +00:00
zmod
Makefile.files	Connect the SHA-512t256 and Skein hashing algorithms to ZFS	2016-05-31 04:12:14 +00:00