sched/cputime: Drop now-stale mul_u64_u64_div_u64() over-approximation guard

Browse source

Commit 77baa5bafc ("sched/cputime: Fix mul_u64_u64_div_u64() precision
for cputime") added a clamp in cputime_adjust():

	if (unlikely(stime > rtime))
		stime = rtime;

The justification was that mul_u64_u64_div_u64() could over-approximate
on some architectures (notably arm64 and the old 32-bit fallback), so
the mathematically impossible stime > rtime was nevertheless reachable
and would underflow utime = rtime - stime.

That premise no longer holds. Commit b29a62d87c ("mul_u64_u64_div_u64:
make it precise always") replaced the fallback implementation with an
exact 128-bit long division, and the x86_64 inline asm already produced
exact results. The helper now returns the mathematically correct
floor(a*b/d) on every architecture, so stime <= rtime is guaranteed by
stime <= stime + utime and the clamp is dead code.

Remove it along with its stale comment.

Signed-off-by: Nicolas Pitre <nico@fluxnic.net>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260514202629.673539-1-nico@fluxnic.net

...

This commit is contained in:

Nicolas Pitre 2026-05-14 16:26:29 -04:00 • committed by Peter Zijlstra

parent eecd5e117c

commit 95f44886af

1 changed files with 0 additions and 6 deletions

Show all changes Ignore whitespace when comparing lines Ignore changes in amount of whitespace Ignore changes in whitespace at EOL

Download patch file Download diff file Expand all files Collapse all files

6

kernel/sched/cputime.c

View file