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- Make prefetch distance adaptive: up to 4MB prefetch doubles for every, hit same as before, but after that it grows by 1/8 every time the prefetch read does not complete in time to satisfy the demand. My tests show that 4MB is sufficient for wide NVMe pool to saturate single reader thread at 2.5GB/s, while new 64MB maximum allows the same thread to reach 1.5GB/s on wide HDD pool. Further distance increase may increase speed even more, but less dramatic and with higher latency. - Allow early reuse of inactive prefetch streams: streams that never saw hits can be reused immediately if there is a demand, while others can be reused after 1s of inactivity, starting with the oldest. After 2s of inactivity streams are deleted to free resources same as before. This allows by several times increase strided read performance on HDD pool in presence of simultaneous random reads, previously filling the zfetch_max_streams limit for seconds and so blocking most of prefetch. - Always issue intermediate indirect block reads with SYNC priority. Each of those reads if delayed for longer may delay up to 1024 other block prefetches, that may be not good for wide pools. Reviewed-by: Allan Jude <allan@klarasystems.com> Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Signed-off-by: Alexander Motin <mav@FreeBSD.org> Sponsored-By: iXsystems, Inc. Closes #13452 |
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