Date: Thu, 16 Apr 2026 15:28:28 +0000 From: Mitchell Horne <mhorne@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-branches@FreeBSD.org Cc: Paulo Fragoso <paulo@nlink.com.br> Subject: git: 928091964581 - stable/15 - hwpmc.4: correct stale default values and update diagnostics Message-ID: <69e1001c.201f8.c9aa4a@gitrepo.freebsd.org>
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The branch stable/15 has been updated by mhorne: URL: https://cgit.FreeBSD.org/src/commit/?id=9280919645816261823f5c4bc5ec6dd19c072e80 commit 9280919645816261823f5c4bc5ec6dd19c072e80 Author: Paulo Fragoso <paulo@nlink.com.br> AuthorDate: 2026-03-23 20:17:54 +0000 Commit: Mitchell Horne <mhorne@FreeBSD.org> CommitDate: 2026-04-16 15:18:25 +0000 hwpmc.4: correct stale default values and update diagnostics The default values documented for kern.hwpmc.logbuffersize (4KB) and kern.hwpmc.nbuffers_pcpu (64) have been incorrect since 2981a3420cb1 (2018), which updated the compiled defaults but did not update the man page. - Correct logbuffersize default from 4KB to 256KB, add 16MB maximum - Correct nbuffers_pcpu default from 64 to 32, document 32MB per-CPU product limit with kern.hwpmc.logbuffersize - Update DIAGNOSTICS section to reflect current warning messages Reviewed by: mhorne MFC after: 1 week Sponsored by: NLINK (nlink.com.br) Differential Revision: https://reviews.freebsd.org/D56050 (cherry picked from commit 2318ea10a3afb66c51078483f74c1a622811a619) --- share/man/man4/hwpmc.4 | 25 +++++++++++++++++++------ 1 file changed, 19 insertions(+), 6 deletions(-) diff --git a/share/man/man4/hwpmc.4 b/share/man/man4/hwpmc.4 index 54a251dcca76..8bb1cb96f694 100644 --- a/share/man/man4/hwpmc.4 +++ b/share/man/man4/hwpmc.4 @@ -441,7 +441,8 @@ The default is 16. The size in kilobytes of each log buffer used by .Nm Ns 's logging function. -The default buffer size is 4KB. +The default buffer size is 256KB. +The maximum value is 16MB. .It Va kern.hwpmc.mincount Pq integer, read-write The minimum sampling rate for sampling mode PMCs. The default count is 1000 events. @@ -449,10 +450,15 @@ The default count is 1000 events. The size of the spin mutex pool used by the PMC driver. The default is 32. .It Va kern.hwpmc.nbuffers_pcpu Pq integer, read-only -The number of log buffers used by +The number of log buffers per CPU used by .Nm for logging. -The default is 64. +The default is 32. +The product of +.Va kern.hwpmc.nbuffers_pcpu +and +.Va kern.hwpmc.logbuffersize +must not exceed 32MB per CPU. .It Va kern.hwpmc.nsamples Pq integer, read-only The number of entries in the per-CPU ring buffer used during sampling. The default is 512. @@ -518,16 +524,23 @@ was not configured with the required configuration option .It "hwpmc: tunable hashsize=%d must be greater than zero." A negative value was supplied for tunable .Va kern.hwpmc.hashsize . -.It "hwpmc: tunable logbuffersize=%d must be greater than zero." +.It "hwpmc: logbuffersize=%d must be greater than zero and less than or equal to %d, resetting to %d." A negative value was supplied for tunable .Va kern.hwpmc.logbuffersize . -.It "hwpmc: tunable nlogbuffers=%d must be greater than zero." +.It "hwpmc: nbuffers_pcpu=%d must be greater than zero, resetting to %d." A negative value was supplied for tunable -.Va kern.hwpmc.nlogbuffers . +.Va kern.hwpmc.nbuffers_pcpu . .It "hwpmc: tunable nsamples=%d out of range." The value for tunable .Va kern.hwpmc.nsamples was negative or greater than 65535. +.It "hwpmc: nbuffers_pcpu=%d * logbuffersize=%d exceeds %dMB per CPU limit, resetting to defaults (%d * %d)." +The product of tunables +.Va kern.hwpmc.nbuffers_pcpu +and +.Va kern.hwpmc.logbuffersize +exceeds the maximum per-CPU memory limit. +Both tunables are reset to their compiled defaults. .El .Sh DEBUGGING Thehome | help
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