+++ /dev/null
-
-Atomic UP test results.
-
-
-
-
-using test-time-probe2.ko
-
-Clock speed : cpu MHz : 3000.077
-
-Tracing inactive
-
-[ 125.787229] test init
-[ 125.787303] test results : time per probe
-[ 125.787306] number of loops : 20000
-[ 125.787309] total time : 204413
-[ 125.787312] test end
-[ 175.660402] test init
-[ 175.660475] test results : time per probe
-[ 175.660479] number of loops : 20000
-[ 175.660482] total time : 203468
-[ 175.660484] test end
-[ 179.337362] test init
-[ 179.337436] test results : time per probe
-[ 179.337440] number of loops : 20000
-[ 179.337443] total time : 204757
-[ 179.337446] test end
-
-Res : 10.21 cycles per loop
-
-Atomic UP, one trace, flight recorder.
-
-[ 357.983971] test init
-[ 357.988837] test results : time per probe
-[ 357.988843] number of loops : 20000
-[ 357.988846] total time : 12349013
-[ 357.988849] test end
-[ 358.718896] test init
-[ 358.723049] test results : time per probe
-[ 358.723053] number of loops : 20000
-[ 358.723057] total time : 12332497
-[ 358.723059] test end
-[ 359.422038] test init
-[ 359.426173] test results : time per probe
-[ 359.426179] number of loops : 20000
-[ 359.426182] total time : 12332535
-[ 359.426185] test end
-
-Res : 616.90 cycles per loop.
-205.63 ns per loop
-
-Atomic SMP, one trace, flight.
-
-
-[ 111.694180] test init
-[ 111.700191] test results : time per probe
-[ 111.700198] number of loops : 20000
-[ 111.700201] total time : 16925670
-[ 111.700204] test end
-[ 112.285716] test init
-[ 112.291321] test results : time per probe
-[ 112.291326] number of loops : 20000
-[ 112.291329] total time : 16766633
-[ 112.291332] test end
-[ 112.880602] test init
-[ 112.884739] test results : time per probe
-[ 112.884743] number of loops : 20000
-[ 112.884746] total time : 12358237
-[ 112.884748] test end
-
-Res : 767.51 cycles per loop
-255.83 ns per loop
-
-(205.63-255.83)/255.83 * 100% = 19.62 %
-
-
-Difference between
-cmpxchg 2967855/20000 = 148.39 cycles or 49.46 ns
-cmpxchg-up 540577/20000 = 27.02 cycles or 9.00 ns
-irq save/restore 12636562/20000 = 631.82 cycles 210.60 ns
-
-
-
-* Memory ordering
-
-offset
-written by local CPU
-read by local CPU and other CPUs (reader)
-
-commit count
-written by local CPU
-read by local CPU and other CPUs (reader)
-
-consumed
-written by any CPU
-read by any CPU
-
-data
-written by local CPU
-read by any CPU
-
-
-test done in the reader :
-if ( consumed < offset )
- if ( subbuf.commit_count == multiple of SUBBUFSIZE)
- read data
- inc consumed
-
-
-We must guarantee the following ordering :
-* offset
-Seen from the local CPU :
-offset must always be incremented before the data is written (already
-consistent)
-
-Seen from other cpus :
-offset and data can be written out of order
-(because offset is always incremented : in an out of order case, offset is lower
-than the actual data ready, but the commit_count _has_ to be incremented to read
-the data (and is preceded by a store fence)
-
-* commit_count
-commit_count must always be seen by other CPUs after the data has been written.
-Therefore, we must put a store fence before the commit_count write. (smp_wmb)
-
-* consumed
-Rarely updated, use LOCK prefix. Acts as a full memory barrier.
-
-
-
-Mathieu Desnoyers, November 2006
projects / lttv.git / blobdiff