From: Qu Wenruo <quwenruo.btrfs@gmx.com>
To: dsterba@suse.cz, Qu Wenruo <wqu@suse.de>,
David Sterba <DSterba@suse.com>,
linux-btrfs@vger.kernel.org
Subject: Re: [PATCH] btrfs: reorder struct btrfs_key for better alignment
Date: Wed, 19 Jun 2019 21:50:58 +0800 [thread overview]
Message-ID: <2f911663-067c-e895-4da5-9fe4b5c1cc35@gmx.com> (raw)
In-Reply-To: <20190619133919.GF8917@twin.jikos.cz>
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On 2019/6/19 下午9:39, David Sterba wrote:
> On Wed, Jun 19, 2019 at 09:37:39AM +0800, Qu Wenruo wrote:
>>> struct btrfs_key {
>>> __u64 objectid;
>>> - __u8 type;
>>> __u64 offset;
>>> + __u8 type;
>>> } __attribute__ ((__packed__));
>>
>> And why not remove the packed attribute?
>
> Because of this (stack usage changes):
That's expected as long as we're using btrfs_key on stack.
But if we're using btrfs_key on stack and follow the packed feature,
then adjacent on stack memory is not accessed aligned, which could cause
(unobvious) performance drop.
If the unaligned memory access is really causing some performance even
on stack memory, then I'd say the bump in stack memory usage is acceptable.
If not, then the idea of default -Waddress-of-packed-member makes no sense.
Thanks,
Qu
>
> do_relocation +8 (304 -> 312)
> btrfs_orphan_cleanup +16 (128 -> 144)
> btrfs_init_new_device -16 (288 -> 272)
> get_subvol_name_from_objectid +8 (136 -> 144)
> log_conflicting_inodes +8 (184 -> 192)
> btrfs_read_chunk_tree +16 (128 -> 144)
> btrfs_recover_relocation +8 (136 -> 144)
> scrub_stripe +16 (536 -> 552)
> btrfs_clone +16 (352 -> 368)
> free_space_next_bitmap +8 (80 -> 88)
> btrfs_find_orphan_roots +16 (112 -> 128)
> find_free_dev_extent_start +8 (160 -> 168)
> btrfs_lookup_extent_info +8 (160 -> 168)
> btrfs_find_item +8 (80 -> 88)
> btrfs_create_pending_block_groups +8 (120 -> 128)
> btrfs_read_block_groups -24 (176 -> 152)
> __remove_from_free_space_tree +8 (120 -> 128)
> check_committed_ref +8 (104 -> 112)
> replay_one_buffer +8 (152 -> 160)
> fixup_inode_link_counts +8 (96 -> 104)
> btrfs_del_csums +8 (192 -> 200)
> btrfs_search_path_in_tree_user +16 (192 -> 208)
> btrfs_lookup_dentry +8 (168 -> 176)
> __add_tree_block +8 (120 -> 128)
> __btrfs_balance +8 (264 -> 272)
> __lookup_free_space_inode +16 (112 -> 128)
> __readahead_hook +16 (168 -> 184)
> btrfs_get_parent +8 (96 -> 104)
> btrfs_run_dev_replace +8 (88 -> 96)
> add_qgroup_item +8 (80 -> 88)
> merge_reloc_root +16 (240 -> 256)
> link_to_fixup_dir +8 (80 -> 88)
> btrfs_insert_orphan_item +8 (64 -> 72)
> btrfs_delete_delayed_items +8 (184 -> 192)
> btrfs_read_qgroup_config +8 (136 -> 144)
> is_extent_unchanged +8 (152 -> 160)
> btrfs_recover_log_trees +24 (192 -> 216)
> btrfs_create_free_space_tree +8 (136 -> 144)
> send_subvol +8 (136 -> 144)
> btrfs_compare_trees +24 (176 -> 200)
> get_first_ref +8 (136 -> 144)
> qgroup_trace_new_subtree_blocks +8 (176 -> 184)
> qgroup_trace_extent_swap +16 (192 -> 208)
> generic_bin_search +8 (160 -> 168)
> replay_one_name +8 (152 -> 160)
> btrfs_print_tree +8 (160 -> 168)
> __create_free_space_inode +8 (112 -> 120)
> copy_items +24 (328 -> 352)
> walk_down_reloc_tree +8 (160 -> 168)
> btrfs_find_next_key +8 (184 -> 192)
> btrfs_del_inode_ref +8 (144 -> 152)
> btrfs_check_node +16 (144 -> 160)
> find_next_devid +8 (88 -> 96)
> btrfs_new_inode +8 (184 -> 192)
> __add_to_free_space_tree +16 (136 -> 152)
> __btrfs_run_delayed_refs +8 (168 -> 176)
> btrfs_qgroup_trace_subtree +8 (224 -> 232)
> btrfs_lookup_csums_range +8 (184 -> 192)
> __btrfs_update_delayed_inode +8 (112 -> 120)
> lookup_inline_extent_backref +8 (184 -> 192)
> find_data_references +8 (152 -> 160)
> replay_dir_deletes +16 (168 -> 184)
> check_leaf +8 (168 -> 176)
> btrfs_ioctl_get_subvol_info +16 (128 -> 144)
> btrfs_insert_inode_ref +8 (152 -> 160)
> btrfs_finish_sprout +8 (152 -> 160)
> build_backref_tree +8 (272 -> 280)
> insert_extent_data_ref +8 (96 -> 104)
> send_clone -24 (160 -> 136)
> insert_tree_block_ref +8 (56 -> 64)
> read_node_slot +8 (88 -> 96)
> btrfs_csum_file_blocks +8 (168 -> 176)
> replace_path +16 (352 -> 368)
> changed_inode +16 (144 -> 160)
> process_all_refs +16 (112 -> 128)
> btrfs_find_root +16 (144 -> 160)
> reada_walk_down +8 (176 -> 184)
> btrfs_insert_xattr_item +8 (136 -> 144)
> maybe_send_hole +8 (152 -> 160)
> btrfs_uuid_scan_kthread +8 (520 -> 528)
> modify_free_space_bitmap +8 (192 -> 200)
> lookup_extent_data_ref +8 (144 -> 152)
> btrfs_run_delayed_refs_for_head +8 (208 -> 216)
> btrfs_search_dir_index_item +8 (112 -> 120)
> btrfs_prev_leaf +16 (88 -> 104)
> may_destroy_subvol +8 (88 -> 96)
> convert_free_space_to_extents +8 (176 -> 184)
> btrfs_quota_enable +8 (128 -> 136)
> remove_block_group_free_space +8 (120 -> 128)
> __btrfs_drop_extents +24 (352 -> 376)
> btrfs_finish_chunk_alloc +16 (192 -> 208)
> log_dir_items +16 (192 -> 208)
> btrfs_log_changed_extents +8 (240 -> 248)
> update_cache_item +8 (112 -> 120)
> extent_from_logical +8 (104 -> 112)
> btrfs_drop_snapshot +8 (176 -> 184)
> btrfs_realloc_node +8 (208 -> 216)
> did_create_dir +8 (88 -> 96)
> add_qgroup_relation_item +8 (80 -> 88)
> find_dir_range +8 (112 -> 120)
> btrfs_verify_level_key +8 (128 -> 136)
> do_walk_down +8 (336 -> 344)
> get_last_extent +8 (88 -> 96)
> add_keyed_refs +8 (168 -> 176)
> read_block_for_search +8 (168 -> 176)
> can_rmdir +8 (120 -> 128)
> btrfs_insert_empty_inode +8 (40 -> 48)
> btrfs_add_root_ref +8 (144 -> 152)
> __btrfs_free_extent +8 (216 -> 224)
> add_all_parents +8 (160 -> 168)
> btrfs_search_path_in_tree +8 (120 -> 128)
> add_new_free_space_info +8 (72 -> 80)
> btrfs_set_inode_index +8 (96 -> 104)
> btrfs_search_forward +8 (128 -> 136)
> insert_balance_item +8 (232 -> 240)
> btrfs_find_one_extref +8 (104 -> 112)
> scrub_raid56_parity +8 (400 -> 408)
> btrfs_real_readdir +8 (192 -> 200)
> btrfs_log_inode_parent +8 (264 -> 272)
> btrfs_listxattr +8 (168 -> 176)
> convert_free_space_to_bitmaps +8 (168 -> 176)
> btrfs_verify_dev_extents +8 (152 -> 160)
> find_next_extent +8 (120 -> 128)
> btrfs_set_item_key_safe +8 (160 -> 168)
> btrfs_mark_extent_written +16 (296 -> 312)
> replay_xattr_deletes +8 (192 -> 200)
> caching_kthread +8 (128 -> 136)
> btrfs_remove_chunk +8 (184 -> 192)
> scrub_print_warning_inode +8 (208 -> 216)
> caching_thread +8 (184 -> 192)
> log_new_dir_dentries +16 (216 -> 232)
> drop_objectid_items +16 (112 -> 128)
> insert_dir_log_key +8 (56 -> 64)
> iterate_dir_item +8 (176 -> 184)
> btrfs_lookup_csum +8 (104 -> 112)
> relocate_tree_blocks +8 (168 -> 176)
> btrfs_build_ref_tree -8 (168 -> 160)
> btrfs_find_highest_objectid +8 (80 -> 88)
> btrfs_insert_dir_item +8 (136 -> 144)
> walk_down_log_tree +8 (176 -> 184)
> btrfs_insert_file_extent +8 (112 -> 120)
> setup_leaf_for_split +8 (120 -> 128)
> btrfs_shrink_device +8 (176 -> 184)
>
> LOST (0):
>
> NEW (544):
> btrfs_relocate_sys_chunks
> find_first_block_group
> add_delayed_refs
> process_leaf
>
> LOST/NEW DELTA: +544
> PRE/POST DELTA: +1840
>
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next prev parent reply other threads:[~2019-06-19 13:51 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-18 14:15 [PATCH] btrfs: reorder struct btrfs_key for better alignment David Sterba
2019-06-18 14:20 ` Nikolay Borisov
2019-06-19 1:37 ` Qu Wenruo
2019-06-19 13:39 ` David Sterba
2019-06-19 13:50 ` Qu Wenruo [this message]
2019-06-19 14:14 ` David Sterba
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