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Re: [Qemu-devel] [PATCH 4/4] qemu-iotests: Add 080 for IO throttling
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] [PATCH 4/4] qemu-iotests: Add 080 for IO throttling |
Date: |
Wed, 29 Jan 2014 15:36:30 +0100 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Wed, Jan 29, 2014 at 04:40:43PM +0800, Fam Zheng wrote:
> This case utilizes qemu-io command "aio_{read,write} -a -q" to verify
> the effectiveness of IO throttling options.
>
> The "-a" option will cause qemu-io requests to be accounted.
>
> It's implemented by driving the vm timer from qtest protocol, so the
> throttling timers are signaled with determinied time duration. Then we
s/determinied/determined/
> +class ThrottleTestCase(iotests.QMPTestCase):
> + image_len = 80 * 1024 * 1024 # MB
> +
> + def blockstats(self, device):
> + result = self.vm.qmp("query-blockstats")
> + for r in result['return']:
> + if r['device'] == device:
> + stat = r['stats']
> + return stat['rd_bytes'], stat['rd_operations'],
> stat['wr_bytes'], stat['wr_operations']
> + raise Exception("Device not found for blockstats: %s" % device)
> +
> + def setUp(self):
> + qemu_img('create', '-f', iotests.imgfmt, test_img, "1G")
> + #self.vm = iotests.VM().add_drive(test_img, "bps=1024,bps_max=1")
Commented out line?
> + self.vm = iotests.VM().add_drive(test_img)
> + self.vm.launch()
> +
> + def tearDown(self):
> + self.vm.shutdown()
> + os.remove(test_img)
> +
> + def do_test_throttle(self, seconds=10, **limits):
> + def check_limit(limit, num):
> + # IO throttling algorithm is discrete, allow 10% error so the
> test
> + # is more deterministic
> + return limit == 0 or num < seconds * limit * 1.1
> +
> + nsec_per_sec = 1000000000
> +
> + limits['bps_max'] = 1
> + limits['iops_max'] = 1
I *think* this trick is to force throttling not to allow bursts? Maybe
a comment would be good to clarify. IIRC when max is 0, burst behavior
is different.
> + ns += seconds * nsec_per_sec
> + self.vm.qtest_cmd("clock_step %d" % ns)
> + # wait for a while to let requests take off
> + time.sleep(1)
sleep() is evil but I'm not sure there is a better way either... :(
- Re: [Qemu-devel] [PATCH 2/4] qemu-iotests: Add VM method qtest_cmd() to iotests.py, (continued)