ement is very significant. We are getting killed by the cacheline bouncing of the files_struct lock here. Writes on ramdisk (ext2) seems to vary just too much to get any meaningful number. Also, With Tridge's thread_perf test on a 4(8)-way (HT) P4 xeon system : 2.6.12-rc5-vanilla : Running test 'readwrite' with 8 tasks Threads 0.34 +/- 0.01 seconds Processes 0.16 +/- 0.00 seconds 2.6.12-rc5-fd : Running test 'readwrite' with 8 tasks Threads 0.17 +/- 0.02 seconds Processes 0.17 +/- 0.02 seconds I repeated the measurements on ramfs (as opposed to ext2 on ramdisk in the earlier measurement) and I got more consistent results from tiobench : 4(8) way xeon P4 ----------------- (lock-free) Test 2.6.12-rc5 Stdev 2.6.12-rc5-fd Stdev ------------------------------------------------------------- Seqread 1282 18.59 1343.6 26.37 Randread 1517 7 2415 34.27 Seqwrite 702.2 5.27 709.46 5.9 Randwrite 846.86 15.15 919.68 21.4 4-way ppc64 ------------ (lock-free) Test 2.6.12-rc5 Stdev 2.6.12-rc5-fd Stdev ------------------------------------------------------------- Seqread 1549 91.16 1569.6 47.2 Randread 1473.6 25.11 1585.4 69.99 Seqwrite 1096.8 20.03 1136 29.61 Randwrite 1189.6 4.04 1275.2 32.96 Also running Tridge's thread_perf test on ppc64 : 2.6.12-rc5-vanilla -------------------- Running test 'readwrite' with 4 tasks Threads 0.20 +/- 0.02 seconds Processes 0.16 +/- 0.01 seconds 2.6.12-rc5-fd -------------------- Running test 'readwrite' with 4 tasks Threads 0.18 +/- 0.04 seconds Processes 0.16 +/- 0.01 seconds The benefits are huge (upto ~60%) in some cases on x86 primarily due to the atomic operations during acquisition of ->file_lock and cache line bouncing in fast path. ppc64 benefits are modest due to LL/SC based locking, but still statistically significant. This patch: RCU head initilizer no longer needs the head varible name since we don't use list.h lists anymore. Signed-off-by: Dipankar Sarma Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds tûxzœ$x