On 2022-02-28 19:58:05 [+0100], Jason A. Donenfeld wrote: > Hi Sebastian, Hi Jason, > I'm actually trying quite hard not to change the details of entropy > gathering for 5.18. There are lots of little arguments for why each … > random.c. So I'd like to minimize changes to the semantics. Right now, > those semantics are: > > A) crng_init==0: pre_init_inject after 64 interrupts. > B) crng_init!=0: mix_pool_bytes after 64 interrupts OR after 1 second > has elapsed. Yes. I double checked, that it was not a recent change during that rework. So yes, lets keep it as is, I just wanted to point that out. … > But all this brings me to what I'm really wondering when reading your > email: do your observations matter? Are you observing a performance or > reliability issue or something like that with those workqueues > pending? Is this whole workqueue approach a mistake and we should > revert it? Or is it still okay, but you were just idly wondering about > that time limit? As you can tell, I'm mostly concerned with not > breaking something by accident. I noticed it because I backported the required patches (not everything from your queue, just the patches I needed to drop mine and have everything working). During testing I noticed that the worker is scheduled more often than I expected and I looked that it is scheduled and not accidentally stops due to a backport that went wrong. And since I got the condition wrong… But you are asking for performance. I run b.sh which does: - unpack a kernel to /dev/shm - build allmodconfig and then invoked it with "perf stat -r 5 -a --table ./b.sh" to get some numbers. I applied your complete queue on top of v5.17-rc6, and the result was: | Performance counter stats for 'system wide' (5 runs): | | 45.502.822,32 msec cpu-clock # 32,014 CPUs utilized ( +- 0,05% ) | 9.479.371 context-switches # 208,419 /sec ( +- 0,08% ) | 839.380 cpu-migrations # 18,455 /sec ( +- 0,38% ) | 624.839.341 page-faults # 13,738 K/sec ( +- 0,00% ) |105.297.794.633.131 cycles # 2,315 GHz ( +- 0,01% ) |77.238.191.940.405 stalled-cycles-frontend # 73,37% frontend cycles idle ( +- 0,01% ) |56.724.314.805.475 stalled-cycles-backend # 53,89% backend cycles idle ( +- 0,02% ) |69.889.082.499.264 instructions # 0,66 insn per cycle | # 1,10 stalled cycles per insn ( +- 0,00% ) |14.670.304.314.265 branches # 322,550 M/sec ( +- 0,00% ) | 561.326.606.978 branch-misses # 3,83% of all branches ( +- 0,02% ) | | # Table of individual measurements: | 1419,113 (-2,247) # | 1422,552 (+1,192) # | 1420,773 (-0,587) # | 1422,362 (+1,002) # | 1422,001 (+0,641) # | | # Final result: | 1421,360 +- 0,641 seconds time elapsed ( +- 0,05% ) Checked a few commit earlier, before the workqueue rework started "random: rewrite header introductory comment": | Performance counter stats for 'system wide' (5 runs): | | 45.508.013,44 msec cpu-clock # 32,034 CPUs utilized ( +- 0,05% ) | 9.456.280 context-switches # 208,017 /sec ( +- 0,11% ) | 837.148 cpu-migrations # 18,415 /sec ( +- 0,30% ) | 624.851.749 page-faults # 13,745 K/sec ( +- 0,00% ) |105.289.268.852.002 cycles # 2,316 GHz ( +- 0,01% ) |77.233.457.186.415 stalled-cycles-frontend # 73,38% frontend cycles idle ( +- 0,02% ) |56.740.014.447.074 stalled-cycles-backend # 53,91% backend cycles idle ( +- 0,02% ) |69.882.802.096.982 instructions # 0,66 insn per cycle | # 1,10 stalled cycles per insn ( +- 0,00% ) |14.670.395.601.080 branches # 322,716 M/sec ( +- 0,00% ) | 560.846.203.691 branch-misses # 3,82% of all branches ( +- 0,01% ) | | # Table of individual measurements: | 1418,288 (-2,347) # | 1420,425 (-0,210) # | 1420,633 (-0,001) # | 1421,665 (+1,030) # | 1422,162 (+1,528) # | | # Final result: | 1420,635 +- 0,669 seconds time elapsed ( +- 0,05% ) and then on v5.17-rc6: | Performance counter stats for 'system wide' (5 runs): | | 45.459.406,05 msec cpu-clock # 32,009 CPUs utilized ( +- 0,04% ) | 9.460.380 context-switches # 208,171 /sec ( +- 0,10% ) | 837.571 cpu-migrations # 18,430 /sec ( +- 0,30% ) | 624.859.326 page-faults # 13,750 K/sec ( +- 0,00% ) |105.247.262.852.106 cycles # 2,316 GHz ( +- 0,01% ) |77.185.603.119.285 stalled-cycles-frontend # 73,34% frontend cycles idle ( +- 0,01% ) |56.688.996.383.094 stalled-cycles-backend # 53,87% backend cycles idle ( +- 0,02% ) |69.883.077.705.602 instructions # 0,66 insn per cycle | # 1,10 stalled cycles per insn ( +- 0,00% ) |14.670.347.661.094 branches # 322,813 M/sec ( +- 0,00% ) | 561.066.414.554 branch-misses # 3,82% of all branches ( +- 0,01% ) | | # Table of individual measurements: | 1418,142 (-2,061) # | 1420,187 (-0,016) # | 1421,242 (+1,039) # | 1420,800 (+0,597) # | 1420,644 (+0,441) # | | # Final result: | 1420,203 +- 0,542 seconds time elapsed ( +- 0,04% ) It does not appear that something stands out. > Regards, > Jason Sebastian
