mirror of
https://github.com/torvalds/linux
synced 2024-10-19 01:39:28 +00:00
3a3947271c
There are a few nits in this function. They could in theory all be separate patches, but that's probably taking small commits too far. 1) I added a brief comment saying what it does. 2) I like to declare pointer parameters "const" where possible for documentation reasons. 3) It uses bitmap_weight(&rand, BITS_PER_LONG) to compute the Hamming weight of a 32-bit random number (giving a random integer with mean 16 and variance 8). Passing by reference in a 64-bit variable is silly; just use hweight32(). 4) Its helper function fract_exp_two is unnecessarily tangled. Gcc can optimize the multiply by (1 << x) to a shift, but it can be written in a much more straightforward way at the cost of one more bit of internal precision. Some analysis reveals that this bit is always available. This shrinks the object code for fract_exp_two(x, 6) from 23 bytes: 0000000000000000 <foo1>: 0: 89 f9 mov %edi,%ecx 2: c1 e9 06 shr $0x6,%ecx 5: b8 01 00 00 00 mov $0x1,%eax a: d3 e0 shl %cl,%eax c: 83 e7 3f and $0x3f,%edi f: d3 e7 shl %cl,%edi 11: c1 ef 06 shr $0x6,%edi 14: 01 f8 add %edi,%eax 16: c3 retq To 19: 0000000000000017 <foo2>: 17: 89 f8 mov %edi,%eax 19: 83 e0 3f and $0x3f,%eax 1c: 83 c0 40 add $0x40,%eax 1f: 89 f9 mov %edi,%ecx 21: c1 e9 06 shr $0x6,%ecx 24: d3 e0 shl %cl,%eax 26: c1 e8 06 shr $0x6,%eax 29: c3 retq (Verified with 0 <= frac_bits <= 8, 0 <= x < 16<<frac_bits; both versions produce the same output.) 5) And finally, the call to bch_get_congested() in check_should_bypass() is separated from the use of the value by multiple tests which could moot the need to compute it. Move the computation down to where it's needed. This also saves a local register to hold the computed value. Signed-off-by: George Spelvin <lkml@sdf.org> Signed-off-by: Coly Li <colyli@suse.de> Signed-off-by: Jens Axboe <axboe@kernel.dk> |
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| .. | ||
| bcache | ||
| persistent-data | ||
| dm-bio-prison-v1.c | ||
| dm-bio-prison-v1.h | ||
| dm-bio-prison-v2.c | ||
| dm-bio-prison-v2.h | ||
| dm-bio-record.h | ||
| dm-bufio.c | ||
| dm-builtin.c | ||
| dm-cache-background-tracker.c | ||
| dm-cache-background-tracker.h | ||
| dm-cache-block-types.h | ||
| dm-cache-metadata.c | ||
| dm-cache-metadata.h | ||
| dm-cache-policy-internal.h | ||
| dm-cache-policy-smq.c | ||
| dm-cache-policy.c | ||
| dm-cache-policy.h | ||
| dm-cache-target.c | ||
| dm-core.h | ||
| dm-crypt.c | ||
| dm-delay.c | ||
| dm-era-target.c | ||
| dm-exception-store.c | ||
| dm-exception-store.h | ||
| dm-flakey.c | ||
| dm-init.c | ||
| dm-integrity.c | ||
| dm-io.c | ||
| dm-ioctl.c | ||
| dm-kcopyd.c | ||
| dm-linear.c | ||
| dm-log-userspace-base.c | ||
| dm-log-userspace-transfer.c | ||
| dm-log-userspace-transfer.h | ||
| dm-log-writes.c | ||
| dm-log.c | ||
| dm-mpath.c | ||
| dm-mpath.h | ||
| dm-path-selector.c | ||
| dm-path-selector.h | ||
| dm-queue-length.c | ||
| dm-raid.c | ||
| dm-raid1.c | ||
| dm-region-hash.c | ||
| dm-round-robin.c | ||
| dm-rq.c | ||
| dm-rq.h | ||
| dm-service-time.c | ||
| dm-snap-persistent.c | ||
| dm-snap-transient.c | ||
| dm-snap.c | ||
| dm-stats.c | ||
| dm-stats.h | ||
| dm-stripe.c | ||
| dm-switch.c | ||
| dm-sysfs.c | ||
| dm-table.c | ||
| dm-target.c | ||
| dm-thin-metadata.c | ||
| dm-thin-metadata.h | ||
| dm-thin.c | ||
| dm-uevent.c | ||
| dm-uevent.h | ||
| dm-unstripe.c | ||
| dm-verity-fec.c | ||
| dm-verity-fec.h | ||
| dm-verity-target.c | ||
| dm-verity.h | ||
| dm-writecache.c | ||
| dm-zero.c | ||
| dm-zoned-metadata.c | ||
| dm-zoned-reclaim.c | ||
| dm-zoned-target.c | ||
| dm-zoned.h | ||
| dm.c | ||
| dm.h | ||
| Kconfig | ||
| Makefile | ||
| md-bitmap.c | ||
| md-bitmap.h | ||
| md-cluster.c | ||
| md-cluster.h | ||
| md-faulty.c | ||
| md-linear.c | ||
| md-linear.h | ||
| md-multipath.c | ||
| md-multipath.h | ||
| md.c | ||
| md.h | ||
| raid0.c | ||
| raid0.h | ||
| raid1-10.c | ||
| raid1.c | ||
| raid1.h | ||
| raid5-cache.c | ||
| raid5-log.h | ||
| raid5-ppl.c | ||
| raid5.c | ||
| raid5.h | ||
| raid10.c | ||
| raid10.h | ||