| Message ID | 20250326155200.39895-1-yury.norov@gmail.com (mailing list archive) |
|---|---|
| State | New |
| Delegated to: | Jeff Johnson |
| Headers | show |
| Series | wifi: carl9170: micro-optimize carl9170_tx_shift_bm() | expand |
Hi, On Wed, Mar 26, 2025 at 4:52 PM Yury Norov <yury.norov@gmail.com> wrote: > > The function calls bitmap_empty() just before find_first_bit(). Both > functions are O(N). Because find_first_bit() returns >= nbits in case of > empty bitmap, the bitmap_empty() test may be avoided. > I looked up bitmap_empty(): <https://web.git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/linux/bitmap.h#n423> apart from the small_const_nbits stuff (which carl9170 likely does not qualify for since from what I remember it's a 128bits bitmap) the function just does: | return find_first_bit(src, nbits) == nbits; so yes, find_first_bit runs twice with same parameters... Unless the compiler is smart enough to detect this and (re-)use the intermediate result later. But I haven't check if this is the case with any current, old or future compilers. Has anyone? Anyway, Sure. > Signed-off-by: Yury Norov <yury.norov@gmail.com> Acked-by: Christian Lamparter <chunkeey@gmail.com> > --- > drivers/net/wireless/ath/carl9170/tx.c | 3 +-- > 1 file changed, 1 insertion(+), 2 deletions(-) > > diff --git a/drivers/net/wireless/ath/carl9170/tx.c b/drivers/net/wireless/ath/carl9170/tx.c > index 0226c31a6cae..b7717f9e1e9b 100644 > --- a/drivers/net/wireless/ath/carl9170/tx.c > +++ b/drivers/net/wireless/ath/carl9170/tx.c > @@ -366,8 +366,7 @@ static void carl9170_tx_shift_bm(struct ar9170 *ar, > if (WARN_ON_ONCE(off >= CARL9170_BAW_BITS)) > return; > > - if (!bitmap_empty(tid_info->bitmap, off)) > - off = find_first_bit(tid_info->bitmap, off); > + off = min(off, find_first_bit(tid_info->bitmap, off)); > > tid_info->bsn += off; > tid_info->bsn &= 0x0fff; > -- > 2.43.0 >
diff --git a/drivers/net/wireless/ath/carl9170/tx.c b/drivers/net/wireless/ath/carl9170/tx.c index 0226c31a6cae..b7717f9e1e9b 100644 --- a/drivers/net/wireless/ath/carl9170/tx.c +++ b/drivers/net/wireless/ath/carl9170/tx.c @@ -366,8 +366,7 @@ static void carl9170_tx_shift_bm(struct ar9170 *ar, if (WARN_ON_ONCE(off >= CARL9170_BAW_BITS)) return; - if (!bitmap_empty(tid_info->bitmap, off)) - off = find_first_bit(tid_info->bitmap, off); + off = min(off, find_first_bit(tid_info->bitmap, off)); tid_info->bsn += off; tid_info->bsn &= 0x0fff;
The function calls bitmap_empty() just before find_first_bit(). Both functions are O(N). Because find_first_bit() returns >= nbits in case of empty bitmap, the bitmap_empty() test may be avoided. Signed-off-by: Yury Norov <yury.norov@gmail.com> --- drivers/net/wireless/ath/carl9170/tx.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-)