From ddc212313f16cd65fcf5e8d9ae223f8374822e4d Mon Sep 17 00:00:00 2001 From: Arnd Bergmann Date: Tue, 16 Jan 2018 16:01:36 +0100 Subject: blkcg: simplify statistic accumulation code Some older compilers (gcc-4.4 through 4.6 in particular) struggle with the way that blkg_rwstat_read() returns a structure, leading to excessive stack usage and rather inefficient code: block/blk-cgroup.c: In function 'blkg_destroy': block/blk-cgroup.c:354:1: error: the frame size of 1296 bytes is larger than 1024 bytes [-Werror=frame-larger-than=] block/cfq-iosched.c: In function 'cfqg_stats_add_aux': block/cfq-iosched.c:753:1: error: the frame size of 1928 bytes is larger than 1024 bytes [-Werror=frame-larger-than=] block/bfq-cgroup.c: In function 'bfqg_stats_add_aux': block/bfq-cgroup.c:299:1: error: the frame size of 1928 bytes is larger than 1024 bytes [-Werror=frame-larger-than=] I also notice that there is no point in using atomic accesses for the local variables, so storing the temporaries in simple 'u64' variables not only avoids the stack usage on older compilers but also improves the object code on modern versions. Fixes: e6269c445467 ("blkcg: add blkg_[rw]stat->aux_cnt and replace cfq_group->dead_stats with it") Acked-by: Tejun Heo Signed-off-by: Arnd Bergmann Signed-off-by: Jens Axboe --- include/linux/blk-cgroup.h | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/include/linux/blk-cgroup.h b/include/linux/blk-cgroup.h index e9825ff57b15..69bea82ebeb1 100644 --- a/include/linux/blk-cgroup.h +++ b/include/linux/blk-cgroup.h @@ -660,12 +660,14 @@ static inline void blkg_rwstat_reset(struct blkg_rwstat *rwstat) static inline void blkg_rwstat_add_aux(struct blkg_rwstat *to, struct blkg_rwstat *from) { - struct blkg_rwstat v = blkg_rwstat_read(from); + u64 sum[BLKG_RWSTAT_NR]; int i; for (i = 0; i < BLKG_RWSTAT_NR; i++) - atomic64_add(atomic64_read(&v.aux_cnt[i]) + - atomic64_read(&from->aux_cnt[i]), + sum[i] = percpu_counter_sum_positive(&from->cpu_cnt[i]); + + for (i = 0; i < BLKG_RWSTAT_NR; i++) + atomic64_add(sum[i] + atomic64_read(&from->aux_cnt[i]), &to->aux_cnt[i]); } -- cgit v1.2.3