very low performance on SCSI disks if device node is in tmpfs

From: Olaf Hering
Date: Tue May 25 2004 - 13:48:46 EST


Any ideas why the location of the device node makes such a big
difference? I always wondered why my firewire is so dog slow with 2.6.
Now I know the reason: /dev is in tmpfs.
I dont see that with IDE disks, only with SCSI.

(none):/# /sbin/hdparm -tT /dev/sdb

/dev/sdb:
Timing buffer-cache reads: 2532 MB in 2.00 seconds = 1264.93 MB/sec
Timing buffered disk reads: 48 MB in 3.12 seconds = 15.41 MB/sec
(none):/# /sbin/hdparm -tT /tmp/sdb

/tmp/sdb:
Timing buffer-cache reads: 2328 MB in 2.00 seconds = 1163.01 MB/sec
Timing buffered disk reads: 82 MB in 3.03 seconds = 27.03 MB/sec

This happens also with 2.6.1-mm kernels. I attach the profile with
devnode in tmpfs and on disk.

--
USB is for mice, FireWire is for men!

sUse lINUX ag, nÃRNBERG
1 .save_remaining_regs 0.0063
1 .DoSyscall 0.0093
8 .handle_irq_event 0.0278
36214 .__iommu_free 79.4167
1 .pSeries_flush_hash_range 0.0013
1 .openpic2_get_irq 0.0147
1 .do_page_fault 0.0007
3 .__wake_up 0.0208
8 .schedule 0.0036
1 .__tasklet_schedule 0.0039
5 .r_start 0.0240
1 .alloc_uid 0.0021
3 .__lock_page_wq 0.0068
5 .wait_on_page_bit_wq 0.0118
3 .unlock_page 0.0208
76 .find_lock_page 0.1131
9 .add_to_page_cache_lru 0.0833
6 .read_cache_page 0.0032
142 .do_generic_mapping_read 0.0625
1 .grab_cache_page_nowait 0.0013
2 .__generic_file_aio_write_nolock 0.0006
3 .mempool_resize 0.0045
4 .mempool_create 0.0092
3 .__free_pages_ok 0.0066
1 .__alloc_pages 0.0009
4 .write_one_page 0.0049
1 .page_cache_readahead 0.0014
6 .force_page_cache_readahead 0.0091
3 .read_cache_pages 0.0030
1 .free_block 0.0022
1 .do_drain 0.0086
2 .__cache_shrink 0.0048
1 .kstrdup_vec 0.0035
2 .slabinfo_write 0.0037
4 .__pagevec_lru_add_active 0.0094
1 .__pagevec_lru_add 0.0026
5 .lru_add_drain 0.0298
5 .__pagevec_release 0.0694
6 .invalidate_complete_page 0.0117
10 .truncate_complete_page 0.0243
3 .truncate_inode_pages 0.0025
1 .unmap_vmas 0.0010
1 .page_remove_rmap 0.0026
1 .shmem_truncate 0.0008
2 .shmem_getpage 0.0005
2 .generic_file_llseek 0.0068
1 .remove_inode_buffers 0.0040
2 .end_bio_bh_io_sync 0.0119
1 .nobh_truncate_page 0.0017
1 .buffer_io_error 0.0114
2 .drop_buffers 0.0026
2 .__find_get_block_slow 0.0033
1 .invalidate_bh_lru 0.0068
1 .__find_get_block 0.0013
3 .__bforget 0.0142
1 .__block_commit_write 0.0026
10 .mark_buffer_dirty_inode 0.0490
4 .block_truncate_page 0.0042
6 .__block_prepare_write 0.0044
3 .block_invalidatepage 0.0063
2 .__bread 0.0060
2 .end_buffer_async_write 0.0042
1 .bio_split 0.0027
6 .bio_check_pages_dirty 0.0101
1 .bio_dirty_fn 0.0021
1 .sync_filesystems 0.0018
1 .bd_release 0.0066
1 .bd_claim 0.0045
1 .pipe_release 0.0028
1 .dput 0.0013
2 .ilookup 0.0069
2 .destroy_inode 0.0079
1 .get_filesystem_list 0.0045
3 .generic_osync_inode 0.0066
1 .reiserfs_read_locked_inode 0.0004
2 .reiserfs_iget 0.0082
1 .reiserfs_fill_super 0.0003
26 .search_by_key 0.0034
3 .reiserfs_delete_solid_item 0.0016
4 .flush_commit_list 0.0017
1 .reiserfs_add_ordered_list 0.0034
4 .do_journal_end 0.0008
2 .do_journal_release 0.0038
1 .reiserfs_in_journal 0.0016
1 .reiserfs_resize 0.0005
1 .memmove 0.0833
4 .__strncpy_from_user 0.0667
3 .bitreverse 0.0174
1482 .crc32_le 4.1167
49 .qsort 0.0407
6 .zlib_inflate_blocks 0.0020
1 .n_tty_ioctl 0.0003
1 .dev_set_rdonly 0.0053
2 .blk_queue_find_tag 0.0417
1 .blk_queue_init_tags 0.0047
1 .blk_queue_invalidate_tags 0.0035
2 .__make_request 0.0010
1 .blk_init_queue 0.0019
9 .blkdev_ioctl 0.0036
1 .bcm5201_suspend 0.0033
11 .scsi_host_lookup 0.0372
8 .__scsi_mode_sense 0.0112
1 .scsi_mode_sense 0.0050
1 .scsi_free_host_dev 0.0038
1 .scsi_alloc_sdev 0.0008
1 .scsi_probe_and_add_lun 0.0003
1 .ata_scsi_slave_config 0.0045
1 .bit_func 0.0417
2 .i2c_stop 0.0030
1 .dev_ethtool 0.0003
1 .tcp_sendmsg 0.0002
1 .inetdev_init 0.0016
38268 total 0.0102
4 .save_remaining_regs 0.0250
1 .DoSyscall 0.0093
35 .handle_irq_event 0.1215
1 .sched_clock 0.0312
1 .__down_interruptible 0.0027
5 .power4_idle 0.0347
37021 .__iommu_free 81.1864
1 .openpic2_get_irq 0.0147
1 .flush_dcache_page 0.0179
5 .__wake_up 0.0347
27 .schedule 0.0122
1 .io_schedule 0.0028
1 .finish_wait 0.0053
2 .prepare_to_wait 0.0106
1 .remove_wait_queue 0.0069
1 .copy_process 0.0002
2 .__tasklet_hi_schedule 0.0078
3 .__tasklet_schedule 0.0117
25 .r_start 0.1202
1 .alloc_uid 0.0021
3 .__lock_page_wq 0.0068
2 .wait_on_page_bit_wq 0.0047
1 .unlock_page 0.0069
75 .find_lock_page 0.1116
1 .add_to_page_cache 0.0014
6 .add_to_page_cache_lru 0.0556
1 .read_cache_page 0.0005
147 .do_generic_mapping_read 0.0647
1 .wait_on_page_writeback_range_wq 0.0015
3 .__generic_file_aio_write_nolock 0.0009
3 .mempool_resize 0.0045
3 .mempool_create 0.0069
1 .setup_per_zone_pages_min 0.0022
1 .__free_pages_ok 0.0022
1 .__alloc_pages 0.0009
1 .write_one_page 0.0012
1 .do_page_cache_readahead 0.0016
6 .read_cache_pages 0.0059
1 .free_block 0.0022
1 .do_drain 0.0086
3 .__cache_shrink 0.0071
1 .__kmalloc 0.0044
1 .__pagevec_lru_add_active 0.0024
2 .lru_add_drain 0.0119
4 .__pagevec_release 0.0556
1 .invalidate_complete_page 0.0020
1 .truncate_complete_page 0.0024
2 .truncate_inode_pages 0.0017
1 .wakeup_kswapd 0.0100
1 .anon_vma_prepare 0.0038
1 .page_remove_rmap 0.0026
1 .unmap_pte_page 0.0009
2 .try_to_unmap_one 0.0014
2 .sys_readv 0.0063
1 .invalidate_inode_buffers 0.0048
1 .nobh_commit_write 0.0069
1 .generic_cont_expand 0.0014
2 .submit_bh 0.0032
1 .__find_get_block_slow 0.0016
2 .mark_buffer_dirty 0.0116
2 .block_invalidatepage 0.0042
1 .end_buffer_async_write 0.0021
1 .match_token 0.0014
2 .__strncpy_from_user 0.0333
4 .bitreverse 0.0233
1542 .crc32_le 4.2833
42 .qsort 0.0349
4 .zlib_inflate_blocks 0.0013
2 .tty_read 0.0044
1 .start_tty 0.0032
1 .blk_rq_map_sg 0.0021
1 .blk_queue_init_tags 0.0047
1 .blk_queue_invalidate_tags 0.0035
4 .__make_request 0.0020
11 .blkdev_ioctl 0.0043
1 .rd_open 0.0042
1 .gem_interrupt 0.0001
1 .scsi_unregister 0.0208
50 .scsi_host_lookup 0.1689
1 .scsi_add_host 0.0023
18 .__scsi_mode_sense 0.0253
3 .scsi_mode_sense 0.0150
13 .scsi_free_host_dev 0.0492
2 .scsi_alloc_sdev 0.0017
1 .scsi_forget_host 0.0046
1 .scsi_probe_and_add_lun 0.0003
1 .keywest_timeout 0.0040
2 .i2c_stop 0.0030
1 .netdev_run_todo 0.0009
1 .qdisc_kill_estimator 0.0030
39145 total 0.0105