https://github.com/torvalds/linux
Revision 87f1369d6e2e820c77cf9eac542eed4dcf036f64 authored by Paolo Valente on 10 July 2013, 13:46:08 UTC, committed by David S. Miller on 11 July 2013, 20:01:07 UTC
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>
1 parent cdbaa0b
Tip revision: 87f1369d6e2e820c77cf9eac542eed4dcf036f64 authored by Paolo Valente on 10 July 2013, 13:46:08 UTC
pkt_sched: sch_qfq: improve efficiency of make_eligible
pkt_sched: sch_qfq: improve efficiency of make_eligible
Tip revision: 87f1369
Kbuild
#
# Kbuild for top-level directory of the kernel
# This file takes care of the following:
# 1) Generate bounds.h
# 2) Generate asm-offsets.h (may need bounds.h)
# 3) Check for missing system calls
#####
# 1) Generate bounds.h
bounds-file := include/generated/bounds.h
always := $(bounds-file)
targets := $(bounds-file) kernel/bounds.s
quiet_cmd_bounds = GEN $@
define cmd_bounds
(set -e; \
echo "#ifndef __LINUX_BOUNDS_H__"; \
echo "#define __LINUX_BOUNDS_H__"; \
echo "/*"; \
echo " * DO NOT MODIFY."; \
echo " *"; \
echo " * This file was generated by Kbuild"; \
echo " *"; \
echo " */"; \
echo ""; \
sed -ne $(sed-y) $<; \
echo ""; \
echo "#endif" ) > $@
endef
# We use internal kbuild rules to avoid the "is up to date" message from make
kernel/bounds.s: kernel/bounds.c FORCE
$(Q)mkdir -p $(dir $@)
$(call if_changed_dep,cc_s_c)
$(obj)/$(bounds-file): kernel/bounds.s Kbuild
$(Q)mkdir -p $(dir $@)
$(call cmd,bounds)
#####
# 2) Generate asm-offsets.h
#
offsets-file := include/generated/asm-offsets.h
always += $(offsets-file)
targets += $(offsets-file)
targets += arch/$(SRCARCH)/kernel/asm-offsets.s
# Default sed regexp - multiline due to syntax constraints
define sed-y
"/^->/{s:->#\(.*\):/* \1 */:; \
s:^->\([^ ]*\) [\$$#]*\([-0-9]*\) \(.*\):#define \1 \2 /* \3 */:; \
s:^->\([^ ]*\) [\$$#]*\([^ ]*\) \(.*\):#define \1 \2 /* \3 */:; \
s:->::; p;}"
endef
quiet_cmd_offsets = GEN $@
define cmd_offsets
(set -e; \
echo "#ifndef __ASM_OFFSETS_H__"; \
echo "#define __ASM_OFFSETS_H__"; \
echo "/*"; \
echo " * DO NOT MODIFY."; \
echo " *"; \
echo " * This file was generated by Kbuild"; \
echo " *"; \
echo " */"; \
echo ""; \
sed -ne $(sed-y) $<; \
echo ""; \
echo "#endif" ) > $@
endef
# We use internal kbuild rules to avoid the "is up to date" message from make
arch/$(SRCARCH)/kernel/asm-offsets.s: arch/$(SRCARCH)/kernel/asm-offsets.c \
$(obj)/$(bounds-file) FORCE
$(Q)mkdir -p $(dir $@)
$(call if_changed_dep,cc_s_c)
$(obj)/$(offsets-file): arch/$(SRCARCH)/kernel/asm-offsets.s Kbuild
$(call cmd,offsets)
#####
# 3) Check for missing system calls
#
always += missing-syscalls
targets += missing-syscalls
quiet_cmd_syscalls = CALL $<
cmd_syscalls = $(CONFIG_SHELL) $< $(CC) $(c_flags) $(missing_syscalls_flags)
missing-syscalls: scripts/checksyscalls.sh $(offsets-file) FORCE
$(call cmd,syscalls)
# Keep these two files during make clean
no-clean-files := $(bounds-file) $(offsets-file)
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