On 1/26/21 11:59 AM, Maxim Mikityanskiy wrote:
> The cited commit introduced a serious regression with SATA write speed,
> as found by bisecting. This patch reverts this commit, which restores
> write speed back to the values observed before this commit.
>
> The performance tests were done on a Helios4 NAS (2nd batch) with 4 HDDs
> (WD8003FFBX) using dd (bs=1M count=2000). "Direct" is a test with a
> single HDD, the rest are different RAID levels built over the first
> partitions of 4 HDDs. Test results are in MB/s, R is read, W is write.
>
> | Direct | RAID0 | RAID10 f2 | RAID10 n2 | RAID6
> ----------------+--------+-------+-----------+-----------+--------
> 9011495c9466 | R:256 | R:313 | R:276 | R:313 | R:323
> (before faulty) | W:254 | W:253 | W:195 | W:204 | W:117
> ----------------+--------+-------+-----------+-----------+--------
> 5ff9f19231a0 | R:257 | R:398 | R:312 | R:344 | R:391
> (faulty commit) | W:154 | W:122 | W:67.7 | W:66.6 | W:67.2
> ----------------+--------+-------+-----------+-----------+--------
> 5.10.10 | R:256 | R:401 | R:312 | R:356 | R:375
> unpatched | W:149 | W:123 | W:64 | W:64.1 | W:61.5
> ----------------+--------+-------+-----------+-----------+--------
> 5.10.10 | R:255 | R:396 | R:312 | R:340 | R:393
> patched | W:247 | W:274 | W:220 | W:225 | W:121
>
> Applying this patch doesn't hurt read performance, while improves the
> write speed by 1.5x - 3.5x (more impact on RAID tests). The write speed
> is restored back to the state before the faulty commit, and even a bit
> higher in RAID tests (which aren't HDD-bound on this device) - that is
> likely related to other optimizations done between the faulty commit and
> 5.10.10 which also improved the read speed.
>
> Signed-off-by: Maxim Mikityanskiy <maxtram95@xxxxxxxxx>
> Fixes: 5ff9f19231a0 ("block: simplify set_init_blocksize")
> Cc: Christoph Hellwig <hch@xxxxxx>
> Cc: Jens Axboe <axboe@xxxxxxxxx>
> ---
> fs/block_dev.c | 10 +++++++++-
> 1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index 3b8963e228a1..235b5042672e 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -130,7 +130,15 @@ EXPORT_SYMBOL(truncate_bdev_range);
>
> static void set_init_blocksize(struct block_device *bdev)
> {
> - bdev->bd_inode->i_blkbits = blksize_bits(bdev_logical_block_size(bdev));
> + unsigned int bsize = bdev_logical_block_size(bdev);
> + loff_t size = i_size_read(bdev->bd_inode);
> +
> + while (bsize < PAGE_SIZE) {
> + if (size & bsize)
> + break;
> + bsize <<= 1;
> + }
> + bdev->bd_inode->i_blkbits = blksize_bits(bsize);
> }
>
> int set_blocksize(struct block_device *bdev, int size)
How can this patch affect write speed? I haven't found any calls of
set_init_blocksize() in the I/O path. Did I perhaps overlook something?
Bart.
