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linuxkernelusb
vleschuk
vleschuk

Reputation: 81

Very low performance of g_mass_storage virtual usb device

Hello I am using Linux usb gadget facility to emulate a USB flash drive. It is working fine except for very low performance.

I use a 4Gb file, created by dd and created a ext2 or vfat (tried both) partition on it. Than I mount it using the following command sequence:

# modprobe dummy_hcd is_super_speed=1 # I tried is_high_speed=1, and no parameter too
# modprobe g_mass_storage file=/home/del/img/flash stall=0 # tried w/o stall=0 too
# mount /dev/sdc1 /mnt/tmp

After that I get /dev/sdc and /dev/sdc1 devices created without any errors in dmesg:

[1256700.986581] usb 3-1: reset high-speed USB device number 5 using dummy_hcd
[1256701.022551]  gadget: high-speed config #1: Linux File-Backed Storage
[1256701.242481] usb 3-1: reset high-speed USB device number 5 using dummy_hcd
[1256701.278422]  gadget: high-speed config #1: Linux File-Backed Storage
[1256701.422339]  gadget: high-speed config #1: Linux File-Backed Storage
[1256934.915697] usb 3-1: reset high-speed USB device number 5 using dummy_hcd
[1256934.951628]  gadget: high-speed config #1: Linux File-Backed Storage
[1256935.915155] usb 3-1: reset high-speed USB device number 5 using dummy_hcd
[1256935.951090]  gadget: high-speed config #1: Linux File-Backed Storage
[1256936.095018]  gadget: high-speed config #1: Linux File-Backed Storage
[1317073.396892] usb-storage 3-1:1.0: Quirks match for vid 0525 pid a4a5: 10000
[1317073.396995] scsi53 : usb-storage 3-1:1.0
[1317074.411883] scsi 53:0:0:0: Direct-Access     Linux    File-CD Gadget   0302 PQ: 0 ANSI: 2
[1317074.412669] sd 53:0:0:0: Attached scsi generic sg3 type 0
[1317074.431910] sd 53:0:0:0: [sdc] 8388608 512-byte logical blocks: (4.29 GB/4.00 GiB)
[1317074.443816] sd 53:0:0:0: [sdc] Write Protect is off
[1317074.443821] sd 53:0:0:0: [sdc] Mode Sense: 0f 00 00 00
[1317074.455839] sd 53:0:0:0: [sdc] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA
[1317074.551757]  sdc: sdc1
[1317074.683704] sd 53:0:0:0: [sdc] Attached SCSI removable disk

The problem is that IO performance is very poor. Writing 200Mb file takes quite a while:

$ ls -lh file
-rw-rw-r-- 1 root del 206M Sep  4 09:34 file
$ time sudo cp file /mnt/tmp/
real    11m59.618s
user    0m0.000s
sys     0m0.260s

Which is about 300K/sec. However the same file on the same system is copied to a real USB flash in less than a minute.

Iotop shows something like this:

 TID  PRIO  USER     DISK READ  DISK WRITE  SWAPIN     IO>    COMMAND                
 9986 be/4 root        0.00 B/s  262.05 K/s  0.00 % 99.86 % cp file /mnt/tmp/
20651 be/4 root       51.77 K/s  238.95 K/s  0.00 % 93.23 % [file-storage]

Can anything be done to improve the performance of g_mass_storage-emulated USB drive?

PS: I am using kernel

$ uname -rm
3.2.0-4-686-pae i686

Upvotes: 4

Views: 4029

Answers (1)

Night User
Night User

Reputation: 41

Same here.

After one night at 6:00 i had a solution for me.

modprobe g_mass_storage file=/home/del/img/flash stall=0 buflen=65536

This made up to 5MByte/sec

modprobe g_mass_storage file=/home/del/img/flash stall=0 nofua=1

This made up to 11MByte/sec

A combination of "buflen" and "nofua" did not really helped. About "nufua" read here: http://lxr.free-electrons.com/source/drivers/usb/gadget/file_storage.c?v=3.5

Ultrasoft /

Upvotes: 4

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