On Sat, 4 Aug 2018, Theodore Y. Ts'o wrote: > On Sat, Aug 04, 2018 at 08:17:06PM +0100, Sami Kerola wrote: > > Try to speed up md5 checksums by using hardware accelerators when they are > > present with use of kernel crypto api. > > > > Reference: http://www.chronox.de/libkcapi/html/ch01s02.html > > Signed-off-by: Sami Kerola <kerolasa@xxxxxx> > > I'm not sure I see the point of this change. Is there a use case you > have in mind where people would be using crypto hash based UUID's > where performance is a concern? In in that case where someone was > trying to create a huge number of crypto hash based UUID's, how much > overhead is there in going through the kernel API if there is *not* a > hardware accelerator present? > > - Ted Hi Dmitry & Ted, I should have told in that commit message part of the motivation was to deprecate util-linux local md5 implementation. But since both of you raised concern about performance I decided to test kernel api and util-linux implementations as close the same way as they are used in libuuid. Executive summary: kernel api is surprisingly slow. The following test is using short input messages (1 to 64 bytes) to md5 functions. I assume most uuid use is in this range. As you can see in perf print out the kernel api is about 10x slower. When inputs are up to 1024 bytes slowdown is about x4. With 10 kilobyte chucks these are about as quick. Maybe I am wrong when thinking most uuid's tend to be based on small inputs, so the slow down is relevant. Thank you both for pointing out the change smelled rats. I did not realize kernel api could be so expensive to use. That said I am no longer in favour of merging this change. /* $ dd if=/dev/urandom of=./test.in count=1 bs=10M $ cat ./test.in >/dev/null # ensure page cache is warm $ perf stat md5-test --kernel-api ./test.in Performance counter stats for 'md5-test --kernel-api ./test.in': 2462.555389 task-clock:u (msec) # 0.963 CPUs utilized 0 context-switches:u # 0.000 K/sec 0 cpu-migrations:u # 0.000 K/sec 56 page-faults:u # 0.023 K/sec 213,119,356 cycles:u # 0.087 GHz 65,763,609 instructions:u # 0.31 insn per cycle 19,412,627 branches:u # 7.883 M/sec 131,530 branch-misses:u # 0.68% of all branches 2.557148339 seconds time elapsed $ perf stat md5-test --util-linux ./test.in Performance counter stats for 'md5-test --util-linux ./test.in': 225.212947 task-clock:u (msec) # 0.998 CPUs utilized 0 context-switches:u # 0.000 K/sec 0 cpu-migrations:u # 0.000 K/sec 57 page-faults:u # 0.253 K/sec 225,921,565 cycles:u # 1.003 GHz 375,010,554 instructions:u # 1.66 insn per cycle 21,918,050 branches:u # 97.321 M/sec 48,356 branch-misses:u # 0.22% of all branches 0.225656336 seconds time elapsed */ #include <getopt.h> #include <linux/if_alg.h> #include <stdio.h> #include <sys/socket.h> #include <sys/types.h> #include <sys/uio.h> #include <unistd.h> #include "c.h" #include "closestream.h" #include "nls.h" #include "strutils.h" #include "uuid.h" #include "xalloc.h" #include "md5.h" struct run_state { unsigned int api; unsigned int seed; size_t max_read; int fd; }; static void __attribute__((__noreturn__)) usage(void) { fputs(USAGE_HEADER, stdout); printf(" %s [options] file\n", program_invocation_short_name); fputs(USAGE_SEPARATOR, stdout); puts("Compare util-linux md5 with kernel crypto api."); fputs(USAGE_OPTIONS, stdout); puts(" -u, --util-linux use util-linux md5 implementation (default)"); puts(" -k, --kernel-api use kernel api"); puts(" -s, --seed <number> srand(seed) value (default: 42)"); puts(" -m, --max <number> maximum read chunk from file (default: 64)"); fputs(USAGE_SEPARATOR, stdout); printf(USAGE_HELP_OPTIONS(24)); printf(USAGE_MAN_TAIL("md5-test(1)")); exit(EXIT_SUCCESS); } static void kernel_api(uuid_t out, const uuid_t ns, char *buf, size_t sz) { int tfmfd; struct sockaddr_alg sa = { .salg_family = AF_ALG, .salg_type = "hash", .salg_name = "md5" }; int opfd = -1, fail = 0; struct iovec const iov[2] = { {.iov_base = (void *)ns, .iov_len = sizeof(uuid_t)}, {.iov_base = (void *)buf, .iov_len = sz} }; tfmfd = socket(AF_ALG, SOCK_SEQPACKET, 0); if (bind(tfmfd, (struct sockaddr *)&sa, sizeof(sa)) < 0) fail = 1; if (!fail && (opfd = accept(tfmfd, NULL, 0)) < 0) fail = 1; if (!fail && writev(opfd, iov, 2) < 0) fail = 1; if (!fail && read(opfd, out, sizeof(uuid_t)) == -1) fail = 1; if (opfd != -1) close(opfd); close(tfmfd); } static void util_linux_md5(uuid_t out, const uuid_t ns, char *buf, size_t sz) { UL_MD5_CTX ctx; char hash[UL_MD5LENGTH]; ul_MD5Init(&ctx); /* hash concatenation of well-known UUID with name */ ul_MD5Update(&ctx, ns, sizeof(uuid_t)); ul_MD5Update(&ctx, (const unsigned char *)buf, sz); ul_MD5Final((unsigned char *)hash, &ctx); memcpy(out, hash, sizeof(uuid_t)); } int main(int argc, char **argv) { struct run_state rst = { .api = 0, .seed = 42, .max_read = 64, .fd = -1 }; static const struct option longopts[] = { { "util-linux", no_argument, NULL, 'u' }, { "kernel-api", no_argument, NULL, 'k' }, { "seed", required_argument, NULL, 's' }, { "max", required_argument, NULL, 'm' }, { "version", no_argument, NULL, 'V' }, { "help", no_argument, NULL, 'h' }, { NULL, 0, NULL, 0 } }; int c; char *buf; uuid_t out; uuid_t ns; atexit(close_stdout); while ((c = getopt_long(argc, argv, "uks:m:Vh", longopts, NULL)) != -1) switch (c) { case 'u': rst.api = 0; break; case 'k': rst.api = 1; break; case 's': rst.seed = strtou32_or_err(optarg, "failed to parse seed"); break; case 'm': rst.max_read = strtou32_or_err(optarg, "failed to parse max chunk"); if (rst.max_read == 0) err(EXIT_FAILURE, "max cannot be zero"); break; case 'V': printf(UTIL_LINUX_VERSION); return EXIT_SUCCESS; case 'h': usage(); default: errtryhelp(EXIT_FAILURE); } argc -= optind; argv += optind; if (0 < argc) { rst.fd = open(argv[0], O_RDONLY); if (rst.fd < 0) err(EXIT_FAILURE, "could not open: %s", argv[0]); } else errx(EXIT_FAILURE, "mandatory file argument missing"); buf = xmalloc(rst.max_read); srand(rst.seed); while(1) { ssize_t sz; sz = (rand() % rst.max_read) + 1; if (read(rst.fd, buf, sz) != sz) break; if (rst.api) kernel_api(out, ns, buf, sz); else util_linux_md5(out, ns, buf, sz); } free(buf); close(rst.fd); return EXIT_SUCCESS; } -- To unsubscribe from this list: send the line "unsubscribe util-linux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
