Discussion:
[fuse-devel] cannot handle too many requests simultaneously in fuse?
Pahome Chen
2017-06-01 09:50:22 UTC
Permalink
I write a program which will create 10 threads in a pool.

Then I will let the 10 threads *read* the same file in the fuse which I
made.

But I saw fuse only handle a few mounts of requests(maybe 1~4 requests) in
debug mode.

I saw the other requests will finish *open* operation but don't enter in *read
*operation.

other requests will go on executing after the before requests finished.

why? I thought fuse will handle all requests almost simultaneously.

Fuse Lib version: 2.9.7
using FUSE kernel interface version: 7.19
command option: -o allow_other -d
--
Best Regards,
pahome
Nikolaus Rath
2017-06-01 17:59:58 UTC
Permalink
Post by Pahome Chen
I write a program which will create 10 threads in a pool.
Then I will let the 10 threads *read* the same file in the fuse which I
made.
But I saw fuse only handle a few mounts of requests(maybe 1~4 requests) in
debug mode.
I saw the other requests will finish *open* operation but don't enter in *read
*operation.
other requests will go on executing after the before requests finished.
why? I thought fuse will handle all requests almost simultaneously.
It depends. From fuse_common.h:

/**
* Indicates that the filesystem supports asynchronous read requests.
*
* If this capability is not requested/available, the kernel will
* ensure that there is at most one pending read request per
* file-handle at any time, and will attempt to order read requests by
* increasing offset.
*
* This feature is enabled by default when supported by the kernel.
*/
#define FUSE_CAP_ASYNC_READ (1 << 0)


Did you enable this?


Best,
-Nikolaus
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Pahome Chen
2017-06-02 01:46:10 UTC
Permalink
yes, I enabled it.
and my command option is *-o allow_other -o async_read -d*

Almost situation fuse handle requests to the same file are below:
1 requests -> 5 requests -> 4 requests
2 requests -> other last requests

only the first 1 or 2 or 3 requests enter *read *section almostly, then
other requests enter *read *section.
Post by Nikolaus Rath
Post by Pahome Chen
I write a program which will create 10 threads in a pool.
Then I will let the 10 threads *read* the same file in the fuse which I
made.
But I saw fuse only handle a few mounts of requests(maybe 1~4 requests)
in
Post by Pahome Chen
debug mode.
I saw the other requests will finish *open* operation but don't enter in
*read
Post by Pahome Chen
*operation.
other requests will go on executing after the before requests finished.
why? I thought fuse will handle all requests almost simultaneously.
/**
* Indicates that the filesystem supports asynchronous read requests.
*
* If this capability is not requested/available, the kernel will
* ensure that there is at most one pending read request per
* file-handle at any time, and will attempt to order read requests by
* increasing offset.
*
* This feature is enabled by default when supported by the kernel.
*/
#define FUSE_CAP_ASYNC_READ (1 << 0)
Did you enable this?
Best,
-Nikolaus
--
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Best Regards,
pahome
Nikolaus Rath
2017-06-03 13:44:13 UTC
Permalink
Post by Pahome Chen
Post by Nikolaus Rath
Post by Pahome Chen
I write a program which will create 10 threads in a pool.
Then I will let the 10 threads *read* the same file in the fuse which I
made.
But I saw fuse only handle a few mounts of requests(maybe 1~4 requests)
in
Post by Pahome Chen
debug mode.
I saw the other requests will finish *open* operation but don't enter in
*read
Post by Pahome Chen
*operation.
other requests will go on executing after the before requests finished.
why? I thought fuse will handle all requests almost simultaneously.
/**
* Indicates that the filesystem supports asynchronous read requests.
*
* If this capability is not requested/available, the kernel will
* ensure that there is at most one pending read request per
* file-handle at any time, and will attempt to order read requests by
* increasing offset.
*
* This feature is enabled by default when supported by the kernel.
*/
#define FUSE_CAP_ASYNC_READ (1 << 0)
Did you enable this?
yes, I enabled it.
and my command option is *-o allow_other -o async_read -d*
Do you have the same problem when you use examples/passthrough_ll?
Post by Pahome Chen
1 requests -> 5 requests -> 4 requests
2 requests -> other last requests
only the first 1 or 2 or 3 requests enter *read *section almostly, then
other requests enter *read *section.
Sorry, I do not understand what you're saying here.

Best,
-Nikolaus
--
GPG Fingerprint: ED31 791B 2C5C 1613 AF38 8B8A D113 FCAC 3C4E 599F

»Time flies like an arrow, fruit flies like a Banana.«
Michael Theall
2017-06-03 15:33:05 UTC
Permalink
Hi Nikolaus,

Sounds like he's saying he's only getting a max of 5 concurrent (read)
requests for a single file, even with async_read. If this is not a
limitation of kernel fuse, I'd say it could be due to relatively small read
requests from the user.

Pahome,

I would suggest you try some code that makes a large read request (like
10MB) via read(2); make sure you're not using fread(3) or iostream or
whatever kind of userspace buffered I/O. Let us know if you make the same
observation.

Regards,
Michael Theall
Post by Pahome Chen
2017-06-02 1:59 GMT+08:00 Nikolaus Rath <
On Jun 01 2017, Pahome Chen <
Post by Pahome Chen
I write a program which will create 10 threads in a pool.
Then I will let the 10 threads *read* the same file in the fuse which
I
Post by Pahome Chen
made.
But I saw fuse only handle a few mounts of requests(maybe 1~4
requests)
in
Post by Pahome Chen
debug mode.
I saw the other requests will finish *open* operation but don't enter
in
*read
Post by Pahome Chen
*operation.
other requests will go on executing after the before requests
finished.
Post by Pahome Chen
why? I thought fuse will handle all requests almost simultaneously.
/**
* Indicates that the filesystem supports asynchronous read requests.
*
* If this capability is not requested/available, the kernel will
* ensure that there is at most one pending read request per
* file-handle at any time, and will attempt to order read requests by
* increasing offset.
*
* This feature is enabled by default when supported by the kernel.
*/
#define FUSE_CAP_ASYNC_READ (1 << 0)
Did you enable this?
yes, I enabled it.
and my command option is *-o allow_other -o async_read -d*
Do you have the same problem when you use examples/passthrough_ll?
1 requests -> 5 requests -> 4 requests
2 requests -> other last requests
only the first 1 or 2 or 3 requests enter *read *section almostly, then
other requests enter *read *section.
Sorry, I do not understand what you're saying here.
Best,
-Nikolaus
--
GPG Fingerprint: ED31 791B 2C5C 1613 AF38 8B8A D113 FCAC 3C4E 599F
»Time flies like an arrow, fruit flies like a Banana.«
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Pahome Chen
2017-06-05 04:52:10 UTC
Permalink
Post by Michael Theall
Sounds like he's saying he's only getting a max of 5 concurrent (read)
requests for a single file, even with async_read. If this is not a
limitation of kernel fuse, I'd say it could be due to relatively small read
requests from the user.
Yes, but the number 5 isn't a fixed number, sometimes is more than 5 and
sometimes isn't.

I would suggest you try some code that makes a large read request (like
Post by Michael Theall
10MB) via read(2); make sure you're not using fread(3) or iostream or
whatever kind of userspace buffered I/O. Let us know if you make the same
observation.
I tried from 50bytes to 2MB by read syscall, it seems the same. Always
handle 1, or 2, or 3 requests first.


Let me introduce my fuse system called *myfs*.
It's a filesystem combined with fuse and cloud. myfs download the file when
someone read the file in order to save disk space.
Now I want to simulate that 10 read requests concurrently happended.
I found that only the 1st read requests enter the *read()* function and
other 9 requests left the *open()* but didn't enter *read() *after I
checked the fuse bebug mode log.

So that make me confused with why only the 1st one handled by fuse? It's
common to all filesystems?

thx
Post by Michael Theall
Hi Nikolaus,
Sounds like he's saying he's only getting a max of 5 concurrent (read)
requests for a single file, even with async_read. If this is not a
limitation of kernel fuse, I'd say it could be due to relatively small read
requests from the user.
Pahome,
I would suggest you try some code that makes a large read request (like
10MB) via read(2); make sure you're not using fread(3) or iostream or
whatever kind of userspace buffered I/O. Let us know if you make the same
observation.
Regards,
Michael Theall
Post by Pahome Chen
Post by Pahome Chen
On Jun 01 2017, Pahome Chen <pahomechen-wBRgh9WMbBA-
Post by Pahome Chen
I write a program which will create 10 threads in a pool.
Then I will let the 10 threads *read* the same file in the fuse
which I
Post by Pahome Chen
Post by Pahome Chen
made.
But I saw fuse only handle a few mounts of requests(maybe 1~4
requests)
Post by Pahome Chen
in
Post by Pahome Chen
debug mode.
I saw the other requests will finish *open* operation but don't
enter in
Post by Pahome Chen
*read
Post by Pahome Chen
*operation.
other requests will go on executing after the before requests
finished.
Post by Pahome Chen
Post by Pahome Chen
why? I thought fuse will handle all requests almost simultaneously.
/**
* Indicates that the filesystem supports asynchronous read requests.
*
* If this capability is not requested/available, the kernel will
* ensure that there is at most one pending read request per
* file-handle at any time, and will attempt to order read requests by
* increasing offset.
*
* This feature is enabled by default when supported by the kernel.
*/
#define FUSE_CAP_ASYNC_READ (1 << 0)
Did you enable this?
yes, I enabled it.
and my command option is *-o allow_other -o async_read -d*
Do you have the same problem when you use examples/passthrough_ll?
Post by Pahome Chen
1 requests -> 5 requests -> 4 requests
2 requests -> other last requests
only the first 1 or 2 or 3 requests enter *read *section almostly, then
other requests enter *read *section.
Sorry, I do not understand what you're saying here.
Best,
-Nikolaus
--
GPG Fingerprint: ED31 791B 2C5C 1613 AF38 8B8A D113 FCAC 3C4E 599F
»Time flies like an arrow, fruit flies like a Banana.«
------------------------------------------------------------
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engaging tech sites, Slashdot.org! http://sdm.link/slashdot
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Best Regards,
pahome
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