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3a3947271c
linux/drivers/md
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George Spelvin 3a3947271c bcache: Clean up bch_get_congested() 
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>
2019-04-24 10:56:27 -06:00
..
bcache bcache: Clean up bch_get_congested() 2019-04-24 10:56:27 -06:00
persistent-data dm block manager: remove redundant unlikely annotation 2019-03-05 14:53:48 -05:00
dm-bio-prison-v1.c dm: adjust structure members to improve alignment 2018-06-08 11:53:14 -04:00
dm-bio-prison-v1.h
dm-bio-prison-v2.c dm: adjust structure members to improve alignment 2018-06-08 11:53:14 -04:00
dm-bio-prison-v2.h
dm-bio-record.h block: replace bi_bdev with a gendisk pointer and partitions index 2017-08-23 12:49:55 -06:00
dm-bufio.c Merge branch 'akpm' (patches from Andrew) 2018-12-28 16:55:46 -08:00
dm-builtin.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
dm-cache-background-tracker.c dm cache background tracker: fix sparse warning 2018-04-30 15:40:40 -04:00
dm-cache-background-tracker.h
dm-cache-block-types.h
dm-cache-metadata.c dm cache metadata: verify cache has blocks in blocks_are_clean_separate_dirty() 2018-12-07 16:04:09 -05:00
dm-cache-metadata.h
dm-cache-policy-internal.h
dm-cache-policy-smq.c dm: remove unnecessary unlikely() around WARN_ON_ONCE() 2018-10-16 14:34:59 -04:00
dm-cache-policy.c
dm-cache-policy.h
dm-cache-target.c dm cache: add support for discard passdown to the origin device 2019-03-05 14:53:52 -05:00
dm-core.h dm: disable DISCARD if the underlying storage no longer supports it 2019-04-04 15:33:59 -04:00
dm-crypt.c for-5.1/block-20190302 2019-03-08 14:12:17 -08:00
dm-delay.c dm: Check for device sector overflow if CONFIG_LBDAF is not set 2018-12-18 09:02:26 -05:00
dm-era-target.c dm: allow targets to return output from messages they are sent 2018-04-03 15:04:10 -04:00
dm-exception-store.c
dm-exception-store.h block: remove CONFIG_LBDAF 2019-04-06 10:48:35 -06:00
dm-flakey.c dm flakey: Properly corrupt multi-page bios. 2018-12-18 09:02:27 -05:00
dm-init.c dm init: fix const confusion for dm_allowed_targets array 2019-04-01 16:16:37 -04:00
dm-integrity.c Linux 5.1-rc5 2019-04-15 08:14:19 -06:00
dm-io.c dm: Use kzalloc for all structs with embedded biosets/mempools 2018-06-05 08:47:43 -06:00
dm-ioctl.c dm: add support to directly boot to a mapped device 2019-03-05 14:53:50 -05:00
dm-kcopyd.c dm kcopyd: Fix bug causing workqueue stalls 2018-12-18 09:02:26 -05:00
dm-linear.c dm: Check for device sector overflow if CONFIG_LBDAF is not set 2018-12-18 09:02:26 -05:00
dm-log-userspace-base.c dm: convert to bioset_init()/mempool_init() 2018-05-30 15:33:32 -06:00
dm-log-userspace-transfer.c
dm-log-userspace-transfer.h
dm-log-writes.c dax: Introduce a ->copy_to_iter dax operation 2018-05-22 23:18:31 -07:00
dm-log.c
dm-mpath.c dm mpath: only flush workqueue when needed 2018-12-18 09:02:25 -05:00
dm-mpath.h
dm-path-selector.c
dm-path-selector.h
dm-queue-length.c dm mpath selector: more evenly distribute ties 2018-01-29 13:44:58 -05:00
dm-raid1.c dm: Check for device sector overflow if CONFIG_LBDAF is not set 2018-12-18 09:02:26 -05:00
dm-raid.c dm: eliminate 'split_discard_bios' flag from DM target interface 2019-02-20 23:24:55 -05:00
dm-region-hash.c - Error path bug fix for overflow tests (Dan) 2018-06-12 18:28:00 -07:00
dm-round-robin.c
dm-rq.c dm: disable DISCARD if the underlying storage no longer supports it 2019-04-04 15:33:59 -04:00
dm-rq.h dm: remove unused _rq_tio_cache and _rq_cache 2019-03-05 14:48:50 -05:00
dm-service-time.c dm mpath selector: more evenly distribute ties 2018-01-29 13:44:58 -05:00
dm-snap-persistent.c dm bufio: move dm-bufio.h to include/linux/ 2018-04-03 15:04:23 -04:00
dm-snap-transient.c
dm-snap.c dm snapshot: don't define direct_access if we don't support it 2019-03-05 14:53:52 -05:00
dm-stats.c mm: convert totalram_pages and totalhigh_pages variables to atomic 2018-12-28 12:11:47 -08:00
dm-stats.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
dm-stripe.c dax: Introduce a ->copy_to_iter dax operation 2018-05-22 23:18:31 -07:00
dm-switch.c dm switch: use struct_size() in kzalloc() 2019-03-05 14:48:51 -05:00
dm-sysfs.c dm: remove legacy request-based IO path 2018-10-11 11:36:09 -04:00
dm-table.c dm table: propagate BDI_CAP_STABLE_WRITES to fix sporadic checksum errors 2019-04-01 16:26:02 -04:00
dm-target.c dm: remove unused macro DM_MOD_NAME_SIZE 2018-04-03 15:04:15 -04:00
dm-thin-metadata.c dm thin: fix passdown_double_checking_shared_status() 2019-01-15 16:10:41 -05:00
dm-thin-metadata.h dm thin: fix passdown_double_checking_shared_status() 2019-01-15 16:10:41 -05:00
dm-thin.c dm thin: add sanity checks to thin-pool and external snapshot creation 2019-03-05 14:53:49 -05:00
dm-uevent.c
dm-uevent.h
dm-unstripe.c dm: Check for device sector overflow if CONFIG_LBDAF is not set 2018-12-18 09:02:26 -05:00
dm-verity-fec.c dm verity fec: remove redundant unlikely annotation 2019-03-05 14:53:48 -05:00
dm-verity-fec.h dm: convert to bioset_init()/mempool_init() 2018-05-30 15:33:32 -06:00
dm-verity-target.c dm verity: log the hash algorithm implementation 2018-12-18 09:02:27 -05:00
dm-verity.h dm verity: add 'check_at_most_once' option to only validate hashes once 2018-04-03 15:04:29 -04:00
dm-writecache.c dm writecache: fix typo in name for writeback_wq 2019-03-05 14:53:51 -05:00
dm-zero.c
dm-zoned-metadata.c dm zoned: fix various dmz_get_mblock() issues 2018-10-18 15:17:03 -04:00
dm-zoned-reclaim.c dm kcopyd: return void from dm_kcopyd_copy() 2018-07-31 17:33:21 -04:00
dm-zoned-target.c dm: eliminate 'split_discard_bios' flag from DM target interface 2019-02-20 23:24:55 -05:00
dm-zoned.h
dm.c dm: disable DISCARD if the underlying storage no longer supports it 2019-04-04 15:33:59 -04:00
dm.h dm: remove legacy request-based IO path 2018-10-11 11:36:09 -04:00
Kconfig dm: add support to directly boot to a mapped device 2019-03-05 14:53:50 -05:00
Makefile dm: add support to directly boot to a mapped device 2019-03-05 14:53:50 -05:00
md-bitmap.c md: use correct types in md_bitmap_print_sb 2019-04-10 15:26:08 -07:00
md-bitmap.h md: Avoid namespace collision with bitmap API 2018-08-01 15:49:39 -07:00
md-cluster.c md-cluster: remove suspend_info 2018-10-18 09:41:25 -07:00
md-cluster.h md-cluster: introduce resync_info_get interface for sanity check 2018-10-18 09:36:35 -07:00
md-faulty.c md: convert to bioset_init()/mempool_init() 2018-05-30 15:33:32 -06:00
md-linear.c md-linear: use struct_size() in kzalloc() 2019-02-04 10:37:11 -08:00
md-linear.h Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/shli/md 2017-11-14 16:07:26 -08:00
md-multipath.c treewide: kzalloc() -> kcalloc() 2018-06-12 16:19:22 -07:00
md-multipath.h md: convert to bioset_init()/mempool_init() 2018-05-30 15:33:32 -06:00
md.c md: return -ENODEV if rdev has no mddev assigned 2019-04-16 09:31:21 -07:00
md.h md: batch flush requests. 2019-04-01 12:11:48 -06:00
raid0.c blkcg: remove bio->bi_css and instead use bio->bi_blkg 2018-12-07 22:26:37 -07:00
raid0.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
raid1-10.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
raid1.c for-5.1/block-20190302 2019-03-08 14:12:17 -08:00
raid1.h md: convert to bioset_init()/mempool_init() 2018-05-30 15:33:32 -06:00
raid5-cache.c md/raid5: fix 'out of memory' during raid cache recovery 2019-01-28 11:44:40 -08:00
raid5-log.h raid5: set write hint for PPL 2019-03-12 10:15:18 -07:00
raid5-ppl.c for-5.1/block-post-20190315 2019-03-16 12:36:39 -07:00
raid5.c md/raid: raid5 preserve the writeback action after the parity check 2019-04-16 14:33:18 -07:00
raid5.h md: convert to kvmalloc 2019-03-12 10:04:02 -07:00
raid10.c md: Fix failed allocation of md_register_thread 2019-03-12 10:15:18 -07:00
raid10.h md: convert to bioset_init()/mempool_init() 2018-05-30 15:33:32 -06:00