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Date: Wed, 27 Nov 2013 11:07:41 +0100 From: Richard Cochran <richardcochran@...il.com> To: John Stultz <john.stultz@...aro.org> Cc: Miroslav Lichvar <mlichvar@...hat.com>, linux-kernel@...r.kernel.org, Prarit Bhargava <prarit@...hat.com> Subject: Re: [PATCH RFC] timekeeping: Fix clock stability with nohz On Tue, Nov 19, 2013 at 03:13:19PM +0100, Richard Cochran wrote: > > In this test, the update rate is once per second. When using longer > intervals, the problem becomes worse. Here is another pair of example runs on an idle system, this time with a 32 second update interval. * Periodic Case CONFIG_HZ_PERIODIC=y CONFIG_NO_HZ=y CONFIG_HZ_1000=y The peak to peak time error is about 600 nanoseconds. sudo ./phc2sys -s eth3 -m -q -l7 -O0 -P0 -I0 -R.03125 phc2sys[118.045]: PI servo: sync interval 32.000 kp 0.022 ki 0.009375 phc2sys[150.045]: sys offset 894205 s0 freq +0 delay 5172 phc2sys[182.045]: sys offset 1416429 s1 freq +16319 delay 5176 phc2sys[214.045]: sys offset 7 s2 freq +16320 delay 5172 phc2sys[246.045]: sys offset 140 s2 freq +16324 delay 5179 phc2sys[278.045]: sys offset 346 s2 freq +16332 delay 5171 phc2sys[310.045]: sys offset 494 s2 freq +16339 delay 5184 phc2sys[342.046]: sys offset 485 s2 freq +16344 delay 5191 phc2sys[374.046]: sys offset 251 s2 freq +16341 delay 5172 phc2sys[406.046]: sys offset 153 s2 freq +16340 delay 5174 phc2sys[438.046]: sys offset 156 s2 freq +16342 delay 5193 phc2sys[470.046]: sys offset 39 s2 freq +16340 delay 5179 phc2sys[502.046]: sys offset 173 s2 freq +16344 delay 5076 phc2sys[534.046]: sys offset 286 s2 freq +16349 delay 5171 phc2sys[566.047]: sys offset 130 s2 freq +16347 delay 5159 phc2sys[598.047]: sys offset -64 s2 freq +16342 delay 5191 phc2sys[630.047]: sys offset 176 s2 freq +16349 delay 5184 phc2sys[662.047]: sys offset 248 s2 freq +16353 delay 5167 phc2sys[694.047]: sys offset 166 s2 freq +16353 delay 5187 phc2sys[726.047]: sys offset 227 s2 freq +16356 delay 5179 phc2sys[758.047]: sys offset 91 s2 freq +16354 delay 5177 phc2sys[790.048]: sys offset -12 s2 freq +16352 delay 5179 phc2sys[822.048]: sys offset -44 s2 freq +16351 delay 5189 phc2sys[854.048]: sys offset -99 s2 freq +16349 delay 5159 phc2sys[886.048]: sys offset 53 s2 freq +16352 delay 5184 phc2sys[918.048]: sys offset 241 s2 freq +16359 delay 5172 phc2sys[950.048]: sys offset 293 s2 freq +16363 delay 5191 phc2sys[982.048]: sys offset -92 s2 freq +16353 delay 5179 phc2sys[1014.048]: sys offset -61 s2 freq +16354 delay 5172 phc2sys[1046.049]: sys offset -42 s2 freq +16354 delay 5186 * NO_HZ CONFIG_NO_HZ_COMMON=y CONFIG_NO_HZ_IDLE=y CONFIG_NO_HZ=y CONFIG_RCU_FAST_NO_HZ=y CONFIG_HZ_250=y The peak to peak time error reaches 9.5 microseconds. sudo ./phc2sys -s eth3 -m -q -l7 -O0 -P0 -I0 -R.03125 phc2sys[2036.649]: PI servo: sync interval 32.000 kp 0.022 ki 0.009375 phc2sys[2068.650]: sys offset 1322846 s0 freq +0 delay 5184 phc2sys[2100.650]: sys offset 1845801 s1 freq +16342 delay 5172 phc2sys[2132.650]: sys offset -643 s2 freq +16322 delay 5197 phc2sys[2164.650]: sys offset 111 s2 freq +16340 delay 5192 phc2sys[2196.650]: sys offset -2110 s2 freq +16271 delay 5174 phc2sys[2228.650]: sys offset 4545 s2 freq +16460 delay 5172 phc2sys[2260.650]: sys offset -3666 s2 freq +16246 delay 5160 phc2sys[2292.651]: sys offset 4454 s2 freq +16465 delay 5183 phc2sys[2324.651]: sys offset -1017 s2 freq +16336 delay 5166 phc2sys[2356.651]: sys offset -1248 s2 freq +16319 delay 5159 phc2sys[2388.651]: sys offset 2824 s2 freq +16435 delay 5174 phc2sys[2420.651]: sys offset -2253 s2 freq +16302 delay 5174 phc2sys[2452.651]: sys offset -431 s2 freq +16338 delay 5186 phc2sys[2484.651]: sys offset 374 s2 freq +16359 delay 5191 phc2sys[2516.652]: sys offset 1198 s2 freq +16389 delay 5176 phc2sys[2548.652]: sys offset -1803 s2 freq +16306 delay 5184 phc2sys[2580.652]: sys offset -295 s2 freq +16336 delay 5179 phc2sys[2612.652]: sys offset 753 s2 freq +16366 delay 5188 phc2sys[2644.652]: sys offset -907 s2 freq +16321 delay 5184 phc2sys[2676.652]: sys offset -128 s2 freq +16337 delay 5111 phc2sys[2708.652]: sys offset -2000 s2 freq +16277 delay 5179 phc2sys[2740.653]: sys offset 2270 s2 freq +16392 delay 5174 phc2sys[2772.653]: sys offset 718 s2 freq +16365 delay 5191 phc2sys[2804.653]: sys offset -1004 s2 freq +16318 delay 5172 phc2sys[2836.653]: sys offset -331 s2 freq +16329 delay 5184 phc2sys[2868.653]: sys offset 1667 s2 freq +16389 delay 5081 phc2sys[2900.653]: sys offset -1154 s2 freq +16316 delay 5192 phc2sys[2932.653]: sys offset 5693 s2 freq +16519 delay 5184 phc2sys[2964.654]: sys offset -3833 s2 freq +16275 delay 5171 Thanks, Richard -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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