Login or Register to Ask a Question and Join Our Community

Sponsored Content
Full Discussion: Lseek implementation
Top Forums UNIX for Dummies Questions & Answers Lseek implementation Post 302554953 by Humudituu on Tuesday 13th of September 2011 12:44:37 PM
Old 09-13-2011
Thank you for your replies.

Quote:
Originally Posted by Corona688
ext4 uses generic_file_llseek for lseek, and I find this implementation for that in fs/read_write.c:
(...)
So really, nothing to it, and the only thing that could be blocking is that mutex...

I think you've saturated the kernel with so many simultaneous system calls to the same inode that they're competing for i_mutex.
(...)
I'm trying to wrap my mind around this... The mutex should be released after the lseek, right? Is the mutex active while writing? Otherwise the behaviour explanied below wouldn't make sense to me, as either lseek while reading would be slow as well or the mutex should be released rather quickly... :S

Quote:
Originally Posted by fpmurphy
(...)

However, the behavior you see if what I would expect. Writes by their very nature are going to take longer than reads. Reads can come from cache. Writes cannot.
I would hardly believe this statement to be generally true as writes can be asynchronous, but that is another story.

The point is that I'm having huge lseek latencies when running a benchmark where 100 threads are writing randomly into files compared to 100 threads randomly reading files:
a) read, lseek, read, lseek, read, lseek,...
mean read latency: ~4ms
mean lseek latency: ~0,001ms
b) write, lseek, write, lseek, ...
mean write latency: ~10ms
mean lseek latency: ~8ms
Smilie
 

10 More Discussions You Might Find Interesting

1. Programming

lseek in c

sir, i used lssek as this lseek(fp,-10,2); i am not getting any output i dont now why can you explan sir.. Thanks in advance, Arunkumar (4 Replies)
Discussion started by: arunkumar_mca
4 Replies

2. Shell Programming and Scripting

Need help on AWK implementation

Hi, I am accepting a string from user. compare this output with the awk output as below... echo "\n\n\tDay : \c" read day awk '{ if($day == $2) { if ($mon == $1) { print "Yes" }}}' syslog.txt I am getting the follwoing error awk: Field $() is not correct. The input line... (5 Replies)
Discussion started by: EmbedUX
5 Replies

3. Programming

Hairy Problem! lseek over 4G

recently my project needs me to lseek a position over 4G size.... i found in linux or unix the parameters are all ulong 32 bits...the limit dooms the movement of a position over 4G I was told that i should lseek64 to meet my need... but i have no idea where i can get the function neither by "man... (8 Replies)
Discussion started by: macroideal
8 Replies

4. Programming

Malloc implementation in C

Hey Guys I am trying to implement the malloc function for my OS class and I am having a little trouble with it. I would be really grateful if I could get some hints on this problem. So I am using a doubly-linked list as my data structure and I have to allocate memory for it (duh...). The... (1 Reply)
Discussion started by: Gambit_b
1 Replies

5. UNIX for Advanced & Expert Users

Malloc Implementation in C

Hey Guys Some of my friends have got together and we are trying to write a basic kernel similar to Linux. I am trying to implement the malloc function in C and I am using a doubly linked list as the primary data structure. I need to allocate memory for this link list (duh...) and I don't feel... (2 Replies)
Discussion started by: rbansal2
2 Replies

6. UNIX for Dummies Questions & Answers

lseek() equivalent

I know there is lseek() function that will allow to write or read from certain position in the file. Is there similar function that will let do same but for array rather then file? (9 Replies)
Discussion started by: joker40
9 Replies

7. UNIX for Dummies Questions & Answers

Understanding lseek

I tried to use lseek system call to determine the number of bytes in a file. To do so, I used open system call with O_APPEND flag to open a file. As lseek returns the current offset so I called lseek for opened file with offset as zero and whence as SEEK_CUR. So I guess it must return the number of... (3 Replies)
Discussion started by: Deepak Raj
3 Replies

8. Programming

what is the main difference between difference between using nonatomic lseek and O_APPEND

I think both write at the end of the file ...... but is there a sharp difference between those 2 instruction ..... thank you this is my 3rd question today forgive me :D (1 Reply)
Discussion started by: fwrlfo
1 Replies

9. AIX

Backup: The lseek call failed

Hi, We are facing issues while backing up our 1205 GB filesystem on LTO5 Tape. During backup the "backup: The lseek call failed." messages were generated, I want to know why these messages were generating AIX version is: 6100-08-00-0000 backup: The date of this level 0 backup is Mon Mar 11... (4 Replies)
Discussion started by: m_raheelahmed
4 Replies

10. Programming

Problem with lseek call.

The following code: int fd; if (fd = open("mem", O_RDONLY) == -1) return 1; if (lseek(fd, 0, SEEK_SET) == -1) { char *buf = malloc(512); buf = strerror(errno); printf("%s\n", buf); return 1; } always returns with "illegal seek"... (2 Replies)
Discussion started by: Sir_Tomasz
2 Replies

LEARN ABOUT FREEBSD

acl_is_trivial_np

ACL_STRIP_NP(3) 					   BSD Library Functions Manual 					   ACL_STRIP_NP(3)

NAME

     acl_is_trivial_np -- determine whether ACL is trivial

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <sys/types.h>
     #include <sys/acl.h>

     int
     acl_is_trivial_np(const acl_t aclp, int *trivialp);

DESCRIPTION

     The acl_is_trivial() function determines whether the ACL pointed to by the argument acl is trivial.  Upon successful completion, the location
     referred to by the argument trivialp will be set to 1, if the ACL aclp points to is trivial, or 0 if it's not.

     ACL is trivial if it can be fully expressed as a file mode without losing any access rules.  For POSIX.1e ACLs, ACL is trivial if it has the
     three required entries, one for owner, one for owning group, and one for other.  For NFSv4 ACLs, ACL is trivial if it is identical to the ACL
     generated by acl_strip_np(3).  Files that have non-trivial ACL have a plus sign appended after mode bits in "ls -l" output.

RETURN VALUES

     The acl_get_tag_type() function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to
     indicate the error.

SEE ALSO

     acl(3), posix1e(3)

STANDARDS

     POSIX.1e is described in IEEE POSIX.1e draft 17.  Discussion of the draft continues on the cross-platform POSIX.1e implementation mailing
     list.  To join this list, see the FreeBSD POSIX.1e implementation page for more information.

HISTORY

     POSIX.1e support was introduced in FreeBSD 4.0.  The acl_is_trivial_np() function was added in FreeBSD 8.0.

AUTHORS

     Edward Tomasz Napierala <trasz@FreeBSD.org>

BSD
								 November 12, 2013							       BSD
All times are GMT -4. The time now is 05:49 AM.
Unix & Linux Forums Content Copyright 1993-2022. All Rights Reserved.
Privacy Policy