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author | Paolo Valente <paolo.valente@unimore.it> | 2013-07-10 15:46:08 +0200 |
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committer | David S. Miller <davem@davemloft.net> | 2013-07-11 22:01:07 +0200 |
commit | 87f1369d6e2e820c77cf9eac542eed4dcf036f64 (patch) | |
tree | 65cbaa15e9378cc680aa2db5b00d99abdfea1a61 /init | |
parent | gso: Update tunnel segmentation to support Tx checksum offload (diff) | |
download | linux-87f1369d6e2e820c77cf9eac542eed4dcf036f64.tar.xz linux-87f1369d6e2e820c77cf9eac542eed4dcf036f64.zip |
pkt_sched: sch_qfq: improve efficiency of make_eligible
In make_eligible, a mask is used to decide which groups must become eligible:
the i-th group becomes eligible only if the i-th bit of the mask (from the
right) is set. The mask is computed by left-shifting a 1 by a given number of
places, and decrementing the result. The shift is performed on a ULL to avoid
problems in case the number of places to shift is higher than 31. On a 32-bit
machine, this is more costly than working on an UL. This patch replaces such a
costly operation with two cheaper branches.
The trick is based on the following fact: in case of a shift of at least 32
places, the resulting mask has at least the 32 less significant bits set,
whereas the total number of groups is lower than 32. As a consequence, in this
case it is enough to just set the 32 less significant bits of the mask with a
cheaper ~0UL. In the other case, the shift can be safely performed on a UL.
Reported-by: David S. Miller <davem@davemloft.net>
Reported-by: David Laight <David.Laight@ACULAB.COM>
Signed-off-by: Paolo Valente <paolo.valente@unimore.it>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'init')
0 files changed, 0 insertions, 0 deletions