Re: Change set based shallow clone

From: Jon Smirl <jonsmirl@gmail.com>
Date: Sep 10, 2006, 18:00 UTC
Message-ID: <9e4733910609101100u515ae6e3seababd5780db715d@mail.gmail.com>
In-Reply-To: <20060910161007.8846.qmail@science.horizon.com>

On 10 Sep 2006 12:10:07 -0400, linux@horizon.com <linux@horizon.com> wrote:

> Actually, Linux has one of the fastest forks around, 100-200 us on
> modern x86.  For large executables, the shared page tables patch (is it
> merged yet?) might help.

Here is the opfile of the kernel

3467889 18.9893 copy_page_range 2190416 11.9941 unmap_vmas 1156011 6.3300 page_fault 887794 4.8613 release_pages 860853 4.7138 page_remove_rmap 633243 3.4675 get_page_from_freelist 398773 2.1836 do_wp_page 344422 1.8860 __mutex_lock_slowpath 280070 1.5336 __handle_mm_fault 241713 1.3236 do_page_fault 238398 1.3054 __d_lookup 236654 1.2959 vm_normal_page

At the time this was measured parsecvs was executing millions of git command using system(command). 40% of the CPU was in the kernel, it stayed that way for hours.

18262372 41.0441 /home/good/vmlinux
 5465741 12.2841 /usr/bin/cvs
 4374336  9.8312 /lib/libc-2.4.so
 3627709  8.1532 /lib/libcrypto.so.0.9.8a
 2494610  5.6066 /usr/bin/oprofiled
 2471238  5.5540 /usr/lib/libz.so.1.2.3
  945349  2.1246 /usr/lib/perl5/5.8.8/i386-linux-thread-multi/CORE/libperl.so
  933646  2.0983 /usr/local/bin/git-read-tree
  758776  1.7053 /usr/local/bin/git-write-tree
  642502  1.4440 /lib/ld-2.4.so
  472903  1.0628 /nvidia
  379254  0.8524 /usr/local/bin/git-pack-objects

Maybe we are looking at the wrong thing, it may be fast to fork a process, is it fast for the process to exit?

-- 
Jon Smirl
jonsmirl@gmail.com