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Subject[RFC][FAT] diren scan profiling report


As I said in "[RFC] FAT dirent scan with hint"
<43024977.7020101@sm.sony.co.jp>, we realized that FAT/VFAT has
poor performance with scanning directory entries.

Per discussions with Ogawa-san, VFAT maintainer, I took profiling data
to seek better solution. Here are results attached.

In short, I would say we need to reduce following factors.
a) number of iterations inside fat_search_long()
b) number of callings to uni16_to_x8()
c) number of callings to fat__get_entry(), for short name scan.

In another E-mail, I'll send revised version patch which use hint
values to scan dirent. That patch would reduce number of iterations
inside fat_search_long() and fat_scan(). Those contributes reductions
above a)-c) factors.


RESULTS:


1-1) Top 10 function consuming time on long file name dir scan
(vfat_lookup) for 4095th LFN entry.

% kd -n 10 /tmp/lfn_kft-a.log
Function Count Time Average Local
----------------------------------- ----- -------- -------- --------
vfat_lookup 1 1242285 1242285 705
vfat_find 1 1241522 1241522 629
fat_search_long 1 1240893 1240893 887490
uni16_to_x8 4209 250222 59 249143
fat_get_entry 765 69908 91 3306
fat__get_entry 762 66602 87 50796
fat_shortname2uni 593 33158 55 11393
fat_short2lower_uni 414 21765 52 20860
fat_bmap 202 13425 66 857
fat_bmap_cluster 201 12568 62 1015

*)To exclude profiling overhead, doesn't count functions < 50usec
**) Remove "inline" from fat/dir.c to count up inline funcs.

1-2) Top 10 function consuming time on short file name dir scan
(fat_scan) for 4095th short file name entry.

% kd -n 10 /tmp/kft-a.log
Function Count Time Average Local
----------------------------------- ----- -------- -------- --------
fat_scan 1 149743 149743 68069
fat_get_short_entry 812 81512 100 11706
fat_get_entry 765 69806 91 3252
fat__get_entry 762 66554 87 50425
fat_bmap 199 13181 66 838
fat_bmap_cluster 198 12343 62 1055
fat_get_cluster 194 11288 58 8481
fat_ent_read 52 2807 53 2583
__getblk 32 2339 73 326
__bread 29 2145 73 598

*)To exclude profiling overhead, doesn't count functions < 50usec
**) Remove "inline" from fat/dir.c to count up inline funcs.


2-1) how to get result 1-1)

% ( cat <<__CONF
new
begin
trigger start entry 0xc00cd904 # vfat_lookup
trigger stop exit 0xc00cd904 # vfat_lookup
filter mintime 50
filter maxtime 0
filter noints
logentries 5000000
end

__CONF
) > /proc/kft

% echo prime > /proc/kft

# mount vtat

% time stat 4095th-shortfilename-entry

real 0m1.351s
user 0m0.007s
sys 0m1.295s

# umount

# get data from /proc/kft_data


2-2) how to get result 1-2)


% ( cat <<__CONF
new
begin
trigger start entry 0xc00c36dc # fat_scan
trigger stop exit 0xc00c36dc # fat_scan
filter mintime 50
filter maxtime 0
filter noints
logentries 5000000
end
__CONF
) > /proc/kft

% echo prime > /proc/kft

# mount msdos

% time stat 4095th-shortname-entry

real 0m0.216s
user 0m0.002s
sys 0m0.200s


# umount

# get data from /proc/kft_data


--
Hiroyuki Machida machida@sm.sony.co.jp
SSW Dept. HENC, Sony Corp.
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