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author | Mauro Carvalho Chehab <mchehab+samsung@kernel.org> | 2018-12-17 10:34:24 -0500 |
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committer | Mauro Carvalho Chehab <mchehab+samsung@kernel.org> | 2018-12-17 10:34:24 -0500 |
commit | 4bd257d884902b81493cf11531915009ab5787cf (patch) | |
tree | bf60af2fb9454154e30b888f7f86a9845ad2c4b7 /block/bfq-iosched.h | |
parent | d2b4387f3bdf016e266d23cf657465f557721488 (diff) | |
parent | 7566ec393f4161572ba6f11ad5171fd5d59b0fbd (diff) |
Merge tag 'v4.20-rc7' into patchwork
Linux 4.20-rc7
* tag 'v4.20-rc7': (403 commits)
Linux 4.20-rc7
scripts/spdxcheck.py: always open files in binary mode
checkstack.pl: fix for aarch64
userfaultfd: check VM_MAYWRITE was set after verifying the uffd is registered
fs/iomap.c: get/put the page in iomap_page_create/release()
hugetlbfs: call VM_BUG_ON_PAGE earlier in free_huge_page()
memblock: annotate memblock_is_reserved() with __init_memblock
psi: fix reference to kernel commandline enable
arch/sh/include/asm/io.h: provide prototypes for PCI I/O mapping in asm/io.h
mm/sparse: add common helper to mark all memblocks present
mm: introduce common STRUCT_PAGE_MAX_SHIFT define
alpha: fix hang caused by the bootmem removal
XArray: Fix xa_alloc when id exceeds max
drm/vmwgfx: Protect from excessive execbuf kernel memory allocations v3
MAINTAINERS: Daniel for drm co-maintainer
drm/amdgpu: drop fclk/gfxclk ratio setting
IB/core: Fix oops in netdev_next_upper_dev_rcu()
dm thin: bump target version
drm/vmwgfx: remove redundant return ret statement
drm/i915: Flush GPU relocs harder for gen3
...
Diffstat (limited to 'block/bfq-iosched.h')
-rw-r--r-- | block/bfq-iosched.h | 51 |
1 files changed, 49 insertions, 2 deletions
diff --git a/block/bfq-iosched.h b/block/bfq-iosched.h index 77651d817ecd..0b02bf302de0 100644 --- a/block/bfq-iosched.h +++ b/block/bfq-iosched.h @@ -196,6 +196,9 @@ struct bfq_entity { /* flag, set to request a weight, ioprio or ioprio_class change */ int prio_changed; + + /* flag, set if the entity is counted in groups_with_pending_reqs */ + bool in_groups_with_pending_reqs; }; struct bfq_group; @@ -448,10 +451,54 @@ struct bfq_data { * bfq_weights_tree_[add|remove] for further details). */ struct rb_root queue_weights_tree; + /* - * number of groups with requests still waiting for completion + * Number of groups with at least one descendant process that + * has at least one request waiting for completion. Note that + * this accounts for also requests already dispatched, but not + * yet completed. Therefore this number of groups may differ + * (be larger) than the number of active groups, as a group is + * considered active only if its corresponding entity has + * descendant queues with at least one request queued. This + * number is used to decide whether a scenario is symmetric. + * For a detailed explanation see comments on the computation + * of the variable asymmetric_scenario in the function + * bfq_better_to_idle(). + * + * However, it is hard to compute this number exactly, for + * groups with multiple descendant processes. Consider a group + * that is inactive, i.e., that has no descendant process with + * pending I/O inside BFQ queues. Then suppose that + * num_groups_with_pending_reqs is still accounting for this + * group, because the group has descendant processes with some + * I/O request still in flight. num_groups_with_pending_reqs + * should be decremented when the in-flight request of the + * last descendant process is finally completed (assuming that + * nothing else has changed for the group in the meantime, in + * terms of composition of the group and active/inactive state of child + * groups and processes). To accomplish this, an additional + * pending-request counter must be added to entities, and must + * be updated correctly. To avoid this additional field and operations, + * we resort to the following tradeoff between simplicity and + * accuracy: for an inactive group that is still counted in + * num_groups_with_pending_reqs, we decrement + * num_groups_with_pending_reqs when the first descendant + * process of the group remains with no request waiting for + * completion. + * + * Even this simpler decrement strategy requires a little + * carefulness: to avoid multiple decrements, we flag a group, + * more precisely an entity representing a group, as still + * counted in num_groups_with_pending_reqs when it becomes + * inactive. Then, when the first descendant queue of the + * entity remains with no request waiting for completion, + * num_groups_with_pending_reqs is decremented, and this flag + * is reset. After this flag is reset for the entity, + * num_groups_with_pending_reqs won't be decremented any + * longer in case a new descendant queue of the entity remains + * with no request waiting for completion. */ - unsigned int num_active_groups; + unsigned int num_groups_with_pending_reqs; /* * Number of bfq_queues containing requests (including the |