Re: Re: can enbd server run in kernel?

i am afraid that my previous email with attachment is blocked, so resend again.

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i wrote a small code to test the mmap performance. and i get some
results different from you. i guess the kernel version may have impact
on it or because of some parameters.

what kernel i use, from a fedora core 2 box
[mingz@whoami mmap]$ uname -a
Linux whoami.localdomain 2.6.8-1.521 #1 Mon Aug 16 09:01:18 EDT 2004
i686 i686 i386 GNU/Linux

test c file attached. compile with 
gcc -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64
test.c

change the len from 1024768 to 1024768*100 do two tests. dd a 600MB file
'test' as the data file.

1) with len = 1MB

[mingz@whoami mmap]$ strace -c ./a.out
execve("./a.out", ["./a.out"], [/* 35 vars */]) = 0
% time     seconds  usecs/call     calls    errors syscall
------ ----------- ----------- --------- --------- ----------------
 26.86    0.000047           9         5           old_mmap
 25.14    0.000044          11         4         1 open
  8.57    0.000015           8         2           mprotect
  8.57    0.000015          15         1           mmap2
  6.86    0.000012          12         1           munmap
  5.71    0.000010           5         2           fstat64
  5.14    0.000009           9         1           read
  4.57    0.000008           4         2           close
  3.43    0.000006           6         1           uname
  2.86    0.000005           5         1           set_thread_area
  2.29    0.000004           4         1           brk
------ ----------- ----------- --------- --------- ----------------
100.00    0.000175                    21         1 total

2) with len = 100MB

[mingz@whoami mmap]$ strace -c ./a.out
execve("./a.out", ["./a.out"], [/* 35 vars */]) = 0
% time     seconds  usecs/call     calls    errors syscall
------ ----------- ----------- --------- --------- ----------------
 26.63    0.000049          12         4         1 open
 26.63    0.000049          10         5           old_mmap
  9.24    0.000017          17         1           mmap2
  8.15    0.000015           8         2           mprotect
  6.52    0.000012          12         1           munmap
  5.43    0.000010           5         2           fstat64
  4.89    0.000009           9         1           read
  4.35    0.000008           4         2           close
  3.26    0.000006           6         1           uname
  2.72    0.000005           5         1           set_thread_area
  2.17    0.000004           4         1           brk
------ ----------- ----------- --------- --------- ----------------
100.00    0.000184                    21         1 total

so there is no big difference on total time.

[mingz@whoami mmap]$ strace ./a.out
execve("./a.out", ["./a.out"], [/* 35 vars */]) = 0
uname({sys="Linux", node="whoami.localdomain", ...}) = 0
brk(0)                                  = 0x8a9d000
open("/etc/ld.so.preload", O_RDONLY)    = -1 ENOENT (No such file or
directory)
open("/etc/ld.so.cache", O_RDONLY)      = 3
fstat64(3, {st_mode=S_IFREG|0644, st_size=58108, ...}) = 0
old_mmap(NULL, 58108, PROT_READ, MAP_PRIVATE, 3, 0) = 0xf6ff1000
close(3)                                = 0
open("/lib/tls/libc.so.6", O_RDONLY)    = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0\300+\300"...,
512) = 512
fstat64(3, {st_mode=S_IFREG|0755, st_size=1459344, ...}) = 0
old_mmap(0xbee000, 1162188, PROT_READ|PROT_EXEC, MAP_PRIVATE, 3, 0) =
0xbee000
old_mmap(0xd04000, 16384, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED,
3, 0x116000) = 0xd04000
old_mmap(0xd08000, 7116, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0xd08000
close(3)                                = 0
old_mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS,
-1, 0) = 0xf6ff0000
mprotect(0xd04000, 4096, PROT_READ)     = 0
mprotect(0xbea000, 4096, PROT_READ)     = 0
set_thread_area({entry_number:-1 -> 6, base_addr:0xf6ff0300,
limit:1048575, seg_32bit:1, contents:0, read_exec_only:0,
limit_in_pages:1, seg_not_present:0, useable:1}) = 0
munmap(0xf6ff1000, 58108)               = 0
open("test", O_RDWR|O_LARGEFILE)        = 3
mmap2(NULL, 102476800, PROT_READ|PROT_WRITE, MAP_SHARED, 3, 0) =
0xf0e35000
exit_group(-253538304)                  = ?

see this mmap2 usage.

not sure if these will change when multiple processes open it.

ming

---------test.c-----------------
#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
 
int main(int argc, char **argv)
{
        int fd;
        char *t;
        int len = 1024768 * 100;
        char *path = "test";
 
        fd = open(path, O_RDWR|O_LARGEFILE);
        if (fd < 0)
                printf("fail to open file\n");
        t = mmap(0, len, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
        if ((long)t == -1)
                printf("fail to mmap");
 
}