I'm trying to find out the reason for these writes to my flash drive.
deathstar> while true
> do
> dmesg|grep sdc|grep WRITE
> sleep 3
> done
[17967.580179] kworker/u4:2(6863): WRITE block 20971648 on sdc1 (8 sectors)
[17967.580206] kworker/u4:2(6863): WRITE block 20971784 on sdc1 (8 sectors)
[17967.580214] kworker/u4:2(6863): WRITE block 20971832 on sdc1 (8 sectors)
[17967.580222] kworker/u4:2(6863): WRITE block 21037080 on sdc1 (8 sectors)
I ran:
perf record -g -a
and then
perf report -s comm
to get
- 0.10% 0.10% kworker/u4:2 ▒
ext4_bio_write_page ▒
strnlen ▒
elv_rqhash_del.isra.5.part.6 ▒
find_get_pages ▒
find_get_pages_tag ▒
scsi_init_io ◆
ext4_mb_use_inode_pa ▒
cpuacct_charge ▒
i915_gem_retire_requests_ring ▒
cfq_insert_request ▒
i915_gem_free_request ▒
__wake_up_bit ▒
i915_gem_object_move_to_inactive ▒
bdi_wakeup_thread_delayed ▒
__test_set_page_writeback ▒
scsi_request_fn ▒
ext4_group_desc_csum ▒
__pagevec_lru_add_fn ▒
clear_page_dirty_for_io ▒
wb_writeback ▒
cfq_service_tree_add ▒
cache_grow ▒
__writeback_inodes_wb
How do i now use: ext4_bio_write_page within systemtap to print various arguments.. how do i even determine what the possible args are? I want to do something like:
> stap -v -e 'probe ext4.ext4_bio_write_page?? { printf("%s %d", ???
and extract something interesting like maybe buffer_size or file_name - i don't know what specifically (i want to go through those functions one by one and look at their signatures).
[please note i'm totally new to this so i may have made some very stupid mistakes]
See the systemtap tutorial section 2.2 "what to print" and section 3.2 "target variables". A brief excerpt:
{ println($$vars) }
prints all variables in scope. $foo$ pretty-prints the foo object, including one level of struct subfields. $foo$$ pretty-prints deeply (subject to MAXSTRINGLEN limits).
# stap -L 'kernel.function("foo")'
will print out the list of variables in scope of function foo.