Al wrote: > > On Sat, Jul 04, 2020 at 09:41:09PM +0200, Miklos Szeredi wrote: > > 1) just leave the first explanation (it's an open + read + close > > equivalent) and leave out the rest > > > > 2) add a loop around the vfs_read() in the code. > > 3) don't bother with the entire thing, until somebody manages to demonstrate > a setup where it does make a real difference (compared to than the obvious > sequence of syscalls, that is). Ehh? System call overead is trivially measurable. https://lwn.net/Articles/814175/ > At which point we'll need to figure out > what's going on and deal with the underlying problem of that setup. Run top? Teach userspace to read 1 page minimum? 192803 read(4, "cpu 3718263 4417 342808 7127674"..., 1024) = 1024 192803 read(4, " 0 21217 21617 21954 10201 15425"..., 1024) = 1024 192803 read(4, " 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0"..., 1024) = 1024 192803 read(4, "", 1024) Teach userspace to pread? 192803 openat(AT_FDCWD, "/proc/uptime", O_RDONLY) = 5 192803 lseek(5, 0, SEEK_SET) = 0 192803 read(5, "47198.56 713699.82\n", 8191) = 19 Rhetorical question: what is harder: ditch the main source of overhead (VFS, seq_file, text) or teach userspace how to read files? Here is open+read /proc/cpuinfo in python2 and python3. Python2 case is terrifying. BTW is there is something broken with seqfiles and record keeping? Why does it return only 2 records per read? Python 3: openat(AT_FDCWD, "/proc/cpuinfo", O_RDONLY|O_CLOEXEC) = 3 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 ioctl(3, TCGETS, 0x7ffe6f1f0850) = -1 ENOTTY (Inappropriate ioctl for device) lseek(3, 0, SEEK_CUR) = 0 ioctl(3, TCGETS, 0x7ffe6f1f0710) = -1 ENOTTY (Inappropriate ioctl for device) lseek(3, 0, SEEK_CUR) = 0 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 read(3, "processor\t: 0\nvendor_id\t: Genuin"..., 8192) = 3038 read(3, "processor\t: 2\nvendor_id\t: Genuin"..., 5154) = 3038 read(3, "processor\t: 4\nvendor_id\t: Genuin"..., 2116) = 2116 read(3, "clmulqdq dtes64 monitor ds_cpl v"..., 8448) = 3966 read(3, "processor\t: 8\nvendor_id\t: Genuin"..., 4482) = 3038 read(3, "processor\t: 10\nvendor_id\t: Genui"..., 1444) = 1444 read(3, "t\t: 64\naddress sizes\t: 46 bits p"..., 16896) = 3116 read(3, "processor\t: 13\nvendor_id\t: Genui"..., 13780) = 3044 read(3, "processor\t: 15\nvendor_id\t: Genui"..., 10736) = 1522 read(3, "", 9214) = 0 Python 2 openat(AT_FDCWD, "/proc/cpuinfo", O_RDONLY) = 3 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 0 lseek(3, 0, SEEK_CUR) = 0 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 read(3, "processor\t: 0\nvendor_id\t: Genuin"..., 1024) = 1024 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 1024 lseek(3, 0, SEEK_CUR) = 1024 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 1024 lseek(3, 0, SEEK_CUR) = 1024 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 1024 lseek(3, 0, SEEK_CUR) = 1024 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 1024 lseek(3, 0, SEEK_CUR) = 1024 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 1024 lseek(3, 0, SEEK_CUR) = 1024 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 1024 lseek(3, 0, SEEK_CUR) = 1024 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 1024 lseek(3, 0, SEEK_CUR) = 1024 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 1024 lseek(3, 0, SEEK_CUR) = 1024 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 1024 lseek(3, 0, SEEK_CUR) = 1024 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 1024 lseek(3, 0, SEEK_CUR) = 1024 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 1024 lseek(3, 0, SEEK_CUR) = 1024 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 1024 lseek(3, 0, SEEK_CUR) = 1024 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 1024 lseek(3, 0, SEEK_CUR) = 1024 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 1024 lseek(3, 0, SEEK_CUR) = 1024 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 1024 lseek(3, 0, SEEK_CUR) = 1024 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 1024 lseek(3, 0, SEEK_CUR) = 1024 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 1024 lseek(3, 0, SEEK_CUR) = 1024 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 1024 lseek(3, 0, SEEK_CUR) = 1024 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 1024 lseek(3, 0, SEEK_CUR) = 1024 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 1024 lseek(3, 0, SEEK_CUR) = 1024 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 1024 lseek(3, 0, SEEK_CUR) = 1024 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 1024 lseek(3, 0, SEEK_CUR) = 1024 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 1024 lseek(3, 0, SEEK_CUR) = 1024 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 1024 lseek(3, 0, SEEK_CUR) = 1024 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 1024 lseek(3, 0, SEEK_CUR) = 1024 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 1024 lseek(3, 0, SEEK_CUR) = 1024 read(3, " cqm_occup_llc cqm_mbm_total cqm"..., 1024) = 1024 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 2048 lseek(3, 0, SEEK_CUR) = 2048 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 2048 lseek(3, 0, SEEK_CUR) = 2048 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 2048 lseek(3, 0, SEEK_CUR) = 2048 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 2048 lseek(3, 0, SEEK_CUR) = 2048 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 2048 lseek(3, 0, SEEK_CUR) = 2048 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 2048 lseek(3, 0, SEEK_CUR) = 2048 read(3, "ebs bts rep_good nopl xtopology "..., 1024) = 1024 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 3072 lseek(3, 0, SEEK_CUR) = 3072 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 3072 lseek(3, 0, SEEK_CUR) = 3072 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 3072 lseek(3, 0, SEEK_CUR) = 3072 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 3072 lseek(3, 0, SEEK_CUR) = 3072 read(3, "ntel\ncpu family\t: 6\nmodel\t\t: 79\n"..., 1024) = 1024 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 4096 lseek(3, 0, SEEK_CUR) = 4096 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 4096 lseek(3, 0, SEEK_CUR) = 4096 read(3, "bm_local dtherm ida arat pln pts"..., 1024) = 1024 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 5120 lseek(3, 0, SEEK_CUR) = 5120 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 5120 lseek(3, 0, SEEK_CUR) = 5120 read(3, "nstop_tsc cpuid aperfmperf pni p"..., 1024) = 1024 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 6144 lseek(3, 0, SEEK_CUR) = 6144 read(3, "del name\t: Intel(R) Xeon(R) CPU "..., 1024) = 1024 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 7168 lseek(3, 0, SEEK_CUR) = 7168 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 7168 lseek(3, 0, SEEK_CUR) = 7168 read(3, "d_clear flush_l1d\nvmx flags\t: vn"..., 1024) = 1024 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 8192 lseek(3, 0, SEEK_CUR) = 8192 read(3, "clmulqdq dtes64 monitor ds_cpl v"..., 1024) = 1024 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 9216 lseek(3, 0, SEEK_CUR) = 9216 read(3, "E5-2620 v4 @ 2.10GHz\nstepping\t: "..., 1024) = 1024 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 10240 lseek(3, 0, SEEK_CUR) = 10240 read(3, "vnmi preemption_timer posted_int"..., 1024) = 1024 read(3, " vmx smx est tm2 ssse3 sdbg fma "..., 1024) = 1024 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 12288 lseek(3, 0, SEEK_CUR) = 12288 read(3, ": 1\nmicrocode\t: 0xb000038\ncpu MH"..., 1024) = 1024 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 13312 lseek(3, 0, SEEK_CUR) = 13312 read(3, "r invvpid ept_x_only ept_ad ept_"..., 1024) = 1024 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 14336 lseek(3, 0, SEEK_CUR) = 14336 read(3, "16 xtpr pdcm pcid dca sse4_1 sse"..., 1024) = 1024 read(3, "\t\t: 1326.352\ncache size\t: 20480 "..., 1024) = 1024 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 16384 lseek(3, 0, SEEK_CUR) = 16384 read(3, "gb flexpriority apicv tsc_offset"..., 1024) = 1024 read(3, "4_2 x2apic movbe popcnt tsc_dead"..., 1024) = 1024 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 18432 lseek(3, 0, SEEK_CUR) = 18432 read(3, "KB\nphysical id\t: 0\nsiblings\t: 16"..., 1024) = 1024 read(3, " vtpr mtf vapic ept vpid unrestr"..., 1024) = 1024 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 20480 lseek(3, 0, SEEK_CUR) = 20480 read(3, "adline_timer aes xsave avx f16c "..., 2048) = 2048 read(3, "estricted_guest vapic_reg vid pl"..., 1024) = 1024 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 lseek(3, 0, SEEK_CUR) = 23552 lseek(3, 0, SEEK_CUR) = 23552 read(3, "16c rdrand lahf_lm abm 3dnowpref"..., 2048) = 770 read(3, "", 1024) = 0 close(3) = 0
