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    SubjectRe: sluggish system responsiveness under higher IO load
    Date
    > I'd suggest that you generate a kernel profile while the sluggishness is
    > happening.

    Done...

    profile 1: (emerge of three huge packages which caused quite some IO)

    ffffffff80232650 __wake_up 23 0.2396
    ffffffff803427a0 vgacon_cursor 23 0.0395
    ffffffff8020ba40 free_hot_cold_page 24 0.0652
    ffffffff8020be90 find_vma 25 0.2232
    ffffffff8020c9b0 __wake_up_bit 25 0.5208
    ffffffff80301800 journal_add_journal_head 25 0.0601
    ffffffff803424e0 vgacon_scroll 26 0.0478
    ffffffff802eb970 __ext3_get_inode_loc 27 0.0312
    ffffffff802fd8e0 journal_dirty_metadata 27 0.0456
    ffffffff80207500 kmem_cache_free 28 0.2917
    ffffffff80211d90 do_select 30 0.0216
    ffffffff8020d420 bit_waitqueue 32 0.1429
    ffffffff8020bbb0 fget_light 34 0.1635
    ffffffff8026b97f thread_return 35 0.1211
    ffffffff80268d50 system_call 36 0.2748
    ffffffff8020a580 kmem_cache_alloc 39 0.6094
    ffffffff8020cae0 vm_normal_page 42 0.2188
    ffffffff8020bf00 __make_request 43 0.0384
    ffffffff8020b600 __find_get_block 47 0.0979
    ffffffff802eb5c0 ext3_mark_iloc_dirty 48 0.0508
    ffffffff8020a0f0 get_page_from_freelist 50 0.0428
    ffffffff802fba50 do_get_write_access 55 0.0382
    ffffffff80209050 __link_path_walk 56 0.0132
    ffffffff803a63a0 scsi_request_fn 57 0.0604
    ffffffff8026b0c0 memcpy 59 0.3352
    ffffffff8020ccf0 __delay 69 2.1562
    ffffffff80208350 __handle_mm_fault 78 0.0269
    ffffffff802075e0 unmap_vmas 93 0.0501
    ffffffff80208ea0 __d_lookup 95 0.2199
    ffffffff8026ad30 clear_page 100 1.7544
    ffffffff80341880 vgacon_set_cursor_size 103 0.4023
    ffffffff8020a920 do_page_fault 105 0.0443
    ffffffff80207560 find_get_page 106 0.9464
    ffffffff80207d20 copy_page_range 111 0.0701
    ffffffff8026ad70 copy_page 157 0.7009
    ffffffff80212cd0 __do_softirq 189 1.0739
    ffffffff803a0430 scsi_dispatch_cmd 459 0.7172
    ffffffff8026afda copy_user_generic_c 854 22.4737
    ffffffff80270e00 default_idle 49571 516.3646
    0000000000000000 total 54590 0.0232

    profile 2: (emerge of recent kernel sources- huge, causes quite some IO too)

    ffffffff8020ff40 generic_permission 57 0.2227
    ffffffff8020ccf0 __delay 58 1.8125
    ffffffff802149a0 rb_insert_color 58 0.2417
    ffffffff802af8b0 free_page_and_swap_cache 63 1.3125
    ffffffff8020ccb0 put_page 66 1.0312
    ffffffff803a63a0 scsi_request_fn 67 0.0710
    ffffffff80234c60 unix_poll 69 0.3920
    ffffffff8020b600 __find_get_block 74 0.1542
    ffffffff80268d50 system_call 81 0.6183
    ffffffff8020e220 memscan 88 1.8333
    ffffffff80224820 __up_read 92 0.5227
    ffffffff802fba50 do_get_write_access 95 0.0660
    ffffffff80207500 kmem_cache_free 99 1.0312
    ffffffff80223d40 find_next_zero_bit 100 0.6944
    ffffffff8020d6a0 strncpy_from_user 103 1.2875
    ffffffff80211d90 do_select 104 0.0747
    ffffffff8020c9b0 __wake_up_bit 117 2.4375
    ffffffff8026b97f thread_return 120 0.4152
    ffffffff8020a580 kmem_cache_alloc 143 2.2344
    ffffffff8026b0c0 memcpy 154 0.8750
    ffffffff8020a0f0 get_page_from_freelist 155 0.1327
    ffffffff8020b260 page_remove_rmap 172 2.6875
    ffffffff80221320 copy_process 175 0.0315
    ffffffff80207560 find_get_page 190 1.6964
    ffffffff8020be90 find_vma 198 1.7679
    ffffffff80211900 do_wp_page 249 0.2132
    ffffffff80209050 __link_path_walk 315 0.0740
    ffffffff8026afda copy_user_generic_c 325 8.5526
    ffffffff80212cd0 __do_softirq 452 2.5682
    ffffffff80208350 __handle_mm_fault 479 0.1654
    ffffffff80208ea0 __d_lookup 510 1.1806
    ffffffff8026ad30 clear_page 519 9.1053
    ffffffff803a0430 scsi_dispatch_cmd 576 0.9000
    ffffffff8020a920 do_page_fault 712 0.3007
    ffffffff8020cae0 vm_normal_page 814 4.2396
    ffffffff8026ad70 copy_page 1929 8.6116
    ffffffff802075e0 unmap_vmas 2362 1.2726
    ffffffff80207d20 copy_page_range 2683 1.6938
    ffffffff80270e00 default_idle 45081 469.5938
    0000000000000000 total 64216 0.0273

    I hope this helps.
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