forked from Minki/linux
919edbadeb
Jan Kara reported a performance regression in dbench that he bisected down to commitbad77c375e("xfs: CIL checkpoint flushes caches unconditionally"). Whilst developing the journal flush/fua optimisations this cache was part of, it appeared to made a significant difference to performance. However, now that this patchset has settled and all the correctness issues fixed, there does not appear to be any significant performance benefit to asynchronous cache flushes. In fact, the opposite is true on some storage types and workloads, where additional cache flushes that can occur from fsync heavy workloads have measurable and significant impact on overall throughput. Local dbench testing shows little difference on dbench runs with sync vs async cache flushes on either fast or slow SSD storage, and no difference in streaming concurrent async transaction workloads like fs-mark. Fast NVME storage. From `dbench -t 30`, CIL scale: clients async sync BW Latency BW Latency 1 935.18 0.855 915.64 0.903 8 2404.51 6.873 2341.77 6.511 16 3003.42 6.460 2931.57 6.529 32 3697.23 7.939 3596.28 7.894 128 7237.43 15.495 7217.74 11.588 512 5079.24 90.587 5167.08 95.822 fsmark, 32 threads, create w/ 64 byte xattr w/32k logbsize create chown unlink async 1m41s 1m16s 2m03s sync 1m40s 1m19s 1m54s Slower SATA SSD storage: From `dbench -t 30`, CIL scale: clients async sync BW Latency BW Latency 1 78.59 15.792 83.78 10.729 8 367.88 92.067 404.63 59.943 16 564.51 72.524 602.71 76.089 32 831.66 105.984 870.26 110.482 128 1659.76 102.969 1624.73 91.356 512 2135.91 223.054 2603.07 161.160 fsmark, 16 threads, create w/32k logbsize create unlink async 5m06s 4m15s sync 5m00s 4m22s And on Jan's test machine: 5.18-rc8-vanilla 5.18-rc8-patched Amean 1 71.22 ( 0.00%) 64.94 * 8.81%* Amean 2 93.03 ( 0.00%) 84.80 * 8.85%* Amean 4 150.54 ( 0.00%) 137.51 * 8.66%* Amean 8 252.53 ( 0.00%) 242.24 * 4.08%* Amean 16 454.13 ( 0.00%) 439.08 * 3.31%* Amean 32 835.24 ( 0.00%) 829.74 * 0.66%* Amean 64 1740.59 ( 0.00%) 1686.73 * 3.09%* Performance and cache flush behaviour is restored to pre-regression levels. As such, we can now consider the async cache flush mechanism an unnecessary exercise in premature optimisation and hence we can now remove it and the infrastructure it requires completely. Fixes:bad77c375e("xfs: CIL checkpoint flushes caches unconditionally") Reported-and-tested-by: Jan Kara <jack@suse.cz> Signed-off-by: Dave Chinner <dchinner@redhat.com> Reviewed-by: Darrick J. Wong <djwong@kernel.org> Signed-off-by: Darrick J. Wong <djwong@kernel.org>
62 lines
1.3 KiB
C
62 lines
1.3 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Copyright (c) 2019 Christoph Hellwig.
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*/
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#include "xfs.h"
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static inline unsigned int bio_max_vecs(unsigned int count)
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{
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return bio_max_segs(howmany(count, PAGE_SIZE));
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}
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int
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xfs_rw_bdev(
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struct block_device *bdev,
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sector_t sector,
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unsigned int count,
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char *data,
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unsigned int op)
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{
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unsigned int is_vmalloc = is_vmalloc_addr(data);
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unsigned int left = count;
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int error;
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struct bio *bio;
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if (is_vmalloc && op == REQ_OP_WRITE)
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flush_kernel_vmap_range(data, count);
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bio = bio_alloc(GFP_KERNEL, bio_max_vecs(left));
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bio_set_dev(bio, bdev);
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bio->bi_iter.bi_sector = sector;
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bio->bi_opf = op | REQ_META | REQ_SYNC;
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do {
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struct page *page = kmem_to_page(data);
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unsigned int off = offset_in_page(data);
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unsigned int len = min_t(unsigned, left, PAGE_SIZE - off);
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while (bio_add_page(bio, page, len, off) != len) {
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struct bio *prev = bio;
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bio = bio_alloc(GFP_KERNEL, bio_max_vecs(left));
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bio_copy_dev(bio, prev);
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bio->bi_iter.bi_sector = bio_end_sector(prev);
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bio->bi_opf = prev->bi_opf;
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bio_chain(prev, bio);
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submit_bio(prev);
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}
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data += len;
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left -= len;
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} while (left > 0);
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error = submit_bio_wait(bio);
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bio_put(bio);
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if (is_vmalloc && op == REQ_OP_READ)
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invalidate_kernel_vmap_range(data, count);
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return error;
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}
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