On 2022-08-15, gwes <[email protected]> wrote: > Unexpected behavior: > When I try to chain three programs together with pipes moving lots > of data spin time goes up on most or all CPUs. > Is this known or expected? > > the chain [shortened] was > find /someplace -maxdepth 2 -type f -name '*.flac' -exec \ > metaflac -list --block-type=VORBIS_COMMENT {} + | \ > awk '{mangle}' | \ > sed -e 's/foo/bar/' | \ > sort -o outfile > > On a slow (1.6GHz 8GB) system with an SSD the spin times went > as high as 50% on all cpus. When that happens the sys times > also go very high rendering the system effectively > unusable. Swap space used = 0. > That system is no longer available for testing. > > This is a simplified example on a Ryzen 3600G w/64MB ram & reasonable > rotating rust: > The test file is 3.6G > Under some test cases the spin times go as high as 20% on two or three CPUs > simultaneously. Those are transient and hard to capture. > I can rerun this using -CURRENT if that would give better information. > > Rsults have been more or less the same 6.9, 7.0, 7.1 > > 11881$ cat m2abc.txz m2abc.txz m2abc.txz | cat | cat | cat > xx
-current looks similar. (I catted /bsd a few times to make a test file, in this case the filesystem is on softraid crypto over nvme). CPU0: 0.0% user, 0.0% nice, 45.1% sys, 15.7% spin, 23.5% intr, 15.7% idle CPU1: 0.0% user, 0.0% nice, 33.3% sys, 41.2% spin, 0.0% intr, 25.5% idle CPU2: 2.0% user, 0.0% nice, 39.2% sys, 23.5% spin, 0.0% intr, 35.3% idle CPU3: 2.0% user, 0.0% nice, 29.4% sys, 27.5% spin, 0.0% intr, 41.2% idle Memory: Real: 5172M/15G act/tot Free: 654M Cache: 6685M Swap: 22M/2048M "yes | cat | cat | cat > xx" doesn't hit it. Don't know if it gives any clues but a flamegraph generated while running the multiple cat pipe on my laptop looks like https://junkpile.org/cat-spin-flame.svg
