Performance hit?

Posted Feb 21, 2025 4:43 UTC (Fri) by bmenrigh (subscriber, #63018)
Parent article: Filesystem support for block sizes larger than the page size

Does this come at a performance cost (CPU-wise, not disk-wise). From the description of the details it sounds like it doesn’t, or the overhead is too tiny to matter.

Performance hit?

Posted Feb 21, 2025 12:18 UTC (Fri) by mcgrof (subscriber, #25917) [Link]

We did measurements of the impact to existing 4k workloads and found the impact to be within the noise. The more interesting things were about how larger block sizes perform against 4k block size workloads, and while that was also found to be within the noise I figured I'd share the old results here [0]. The more interesting results were found once one started to use unbounded IO devices such as pmem [0], part of which lead to last year's LSFMM topic to "Measuring and improving buffered I/O". One of the key conclusions of that discussion was the prospect of parallelizing writeback, a topic which has been proposed for this year's LSFMM [2] and for which there are RFC patches out to help review.

[0] https://docs.google.com/presentation/d/e/2PACX-1vS6jYbdGD...
[1] https://lwn.net/Articles/976856/
[2] https://lore.kernel.org/all/Z6GAYFN3foyBlUxK@dread.disast...