Date: Thu, 24 Mar 2005 23:21:54 -0800 (PST) From: Yan Yu <yanyu@CS.UCLA.EDU> To: freebsd-hackers@freebsd.org Subject: a Q on measuring system performance. Message-ID: <Pine.GSO.4.58.0503242211100.5835@panther.cs.ucla.edu> In-Reply-To: <20050319.230230.35850068.imp@bsdimp.com> References: <20050318160528.GQ51688@smp500.sitetronics.com> <20050319080215.GX51688@smp500.sitetronics.com> <20050319.230230.35850068.imp@bsdimp.com>
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Hello, all,
I add some codes in various places relating to file operations inside the
kernel, e.g., fdalloc(), fdused(), fdunused(), fdfree() etc.
I am trying to measure the overhead added by these instrumentation code.
my plan is:
in my user space program, i have something like the following:
--------------------------------------------
gettimeofday(&prev_time, NULL);
for (i=0; i< 1000; i++)
{
fd = fopen("tmp", "r" );
if (fd == NULL)
{
break;
}
cnt ++;
}
gettimeofday(&cur_time, NULL);
t_lapse= misc_tv_offset( &cur_time, &prev_time );
----------------------------------------------------
I would run this for the unmodified kernel, and instrumented kernel.
compare the t_lapse, my concern is that t_lapse includes context switch
time when the user process is taken out of run queue.
I also run "gprof" on the program, some related data is:
% cumulative self self total
time seconds seconds calls ms/call ms/call name
80.0 0.01 0.01 1000 0.01 0.01 __sys_open [3]
20.0 0.01 0.00 1000 0.00 0.00 __sfp [4]
0.0 0.01 0.00 1987 0.00 0.00 memcpy [6]
0.0 0.01 0.00 1000 0.00 0.00 __sflags [283]
0.0 0.01 0.00 1000 0.00 0.01 fopen [1]
i am wonderinf should I better trust gprof instead? so 0.01 ms/call for
related file operation is the result.
or is there some other better way to achieve this?
Many thanks in advance!
yan
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