I would want tests of all the posix operations. Need a difference not
just in throughput, but in max iops for the various ops.
On 07/27/2014 08:27 AM, Vipul Nayyar wrote:
Hi
As guided by you, I performed the experiment regarding measurement of
the effect of always enabled profiling. I performed two write tests,
one with a 20 MB file and the other with a 730 MB file. Each file was
written 20 times to the mounted volume after clearing the buffers on
every iteration and the time taken measured with the time command. I
ran the following bash script for this purpose.
i=1
while [[ $i -lt 21 ]]; do
sync echo 3 /proc/sys/vm/drop_caches
path=/mnt/write_test$i
out=$( time cp /home/vipul/test.avi $path)
i=$((i+1))
done
Since the values at different times for writing the same file are
quite varied, I plotted a graph using the obtained values(Y-axis
represents seconds) which can be found attached. As you might see in
these images, there is no clear pattern found in the variation of
values obtained while writing.
So according to me, values in both the conditions are quite near to
each other and equally capable of going quite high or low than the
mean value and hence, there is no negative effect seen due to the
change proposed. I hope someone else can shed more light on whether
setting the option(always enabled profiling) really decreased the
performance or not.
Regards
Vipul Nayyar
On Wednesday, 16 July 2014 12:50 PM, Krishnan Parthasarathi
kpart...@redhat.com wrote:
Vipul,
Hello,
Following is a proposal for modifying the io profiling capability
of the io-stats xlator. I recently sent in a
patch(review.gluster.org/#/c/8244/) regarding that, which uses the
already written latency related functions in io-stats to dump info
through meta and added some more data containers which would track
some more fops related info each time a request goes through
io-stats. Currently, before the io-stats' custom latency functions
can run, the measure_latency and count_fop_hits option should be
enabled. I propose to remove these two options entirely from io-stats.
In order to track io performance, these options should be enabled
all the time, or removed entirely, so that a record of io requests
can be kept since mount time, else enabling these options only
when it is required will not give you the average statistics over
the whole period since the start. This is based on the methodology
of Linux kernel itself, since it internally maintains the io
statistics data structures all the time and presents it via /proc
filesystem whenever required. Enabling of any option is not
required, and the data available represents statistics since the
boot time.
I would like to know the views over this, if having io-stats
profiling info available all the time would be a good thing?
Could you run the following experiment to measure the effect of
profiling being enabled always?
- Fix the I/O workload to be run.
- Setup 1 (control group) : Run the fixed workload on a volume with
both the profiling options NOT set.
- Setup 2 : Run the (same) fixed workload on the same volume with the
profiling options set.
- In both setup, measure the latencies observed by the said workload.
You could use time(1) command
for a crude measurement.
This should allow us to make an informed decision on whether there is
any performance effect
when profiling is enabled on a volume by default.
Apart from this, I was going over latency.c in libglusterfs, which
does a fine job of maintaining latency info for every xlator and
encountered an anomaly which I thought should be dealt with. The
function gf_proc_dump_latency_info which dumps the latency array
for the specified xlator consists of a last line which in the end
flushes this array through memset after every dump. That means,
you get different latency info every time you read the profile
file in meta. I think, flushing the data structure after every
dump is wrong since, you don't get overall stats since one enabled
the option at the top of meta, and more importantly, multiple
applications reading this file can get wrong info, since it gets
cleared after one read only.
Clearing of the statistics on every request sounds incorrect to me.
Could you please send a patch to fix this?
thanks,
Krish
If my reasons seem apt for you, I'll send a patch over for evaluation.
Regards
Vipul Nayyar
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