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| author | Kalesh Singh <[email protected]> | 2021-10-29 23:24:10 +0000 |
|---|---|---|
| committer | Steven Rostedt (VMware) <[email protected]> | 2021-11-02 00:45:11 +0000 |
| commit | 8b5d46fd7a3892a2e71c9ba6330f1b46d533d0a0 (patch) | |
| tree | b327ba1d4003b14283af9b70d6091e03909519af /lib/string_helpers.c | |
| parent | tracing/osnoise: Remove PREEMPT_RT ifdefs from inside functions (diff) | |
| download | kernel-8b5d46fd7a3892a2e71c9ba6330f1b46d533d0a0.tar.gz kernel-8b5d46fd7a3892a2e71c9ba6330f1b46d533d0a0.zip | |
tracing/histogram: Optimize division by constants
If the divisor is a constant use specific division functions to
avoid extra branches when the trigger is hit.
If the divisor constant but not a power of 2, the division can be
replaced with a multiplication and shift in the following case:
Let X = dividend and Y = divisor.
Choose Z = some power of 2. If Y <= Z, then:
X / Y = (X * (Z / Y)) / Z
(Z / Y) is a constant (mult) which is calculated at parse time, so:
X / Y = (X * mult) / Z
The division by Z can be replaced by a shift since Z is a power of 2:
X / Y = (X * mult) >> shift
As long, as X < Z the results will not be off by more than 1.
Link: https://lkml.kernel.org/r/[email protected]
Suggested-by: Steven Rostedt <[email protected]>
Signed-off-by: Kalesh Singh <[email protected]>
Signed-off-by: Steven Rostedt (VMware) <[email protected]>
Diffstat (limited to 'lib/string_helpers.c')
0 files changed, 0 insertions, 0 deletions