Messages in this thread | | | Date | Thu, 10 Jul 2003 12:04:17 +0200 (CEST) | From | Etienne Lorrain <> | Subject | memset (was: Redundant memset in AIO read_events) |
| |
Note that using memset() is better reserved to initialise variable-size structures or buffers. Even if memset() is extremely optimised, it is still not as fast as not doing anything.
read_events(...) { struct io_event ent; memset(&ent, 0, sizeof(ent)); while (...) { aio_read_evt(ctx, &ent); } ... }
Should be written (when "ent" has to be cleared): read_events(...) { struct io_event ent = {}; while (...) { aio_read_evt(ctx, &ent); } ... }
Just compare the code generated by (using GCC): struct io_event ent; memset(&ent, 0, sizeof(ent)); ent.data = 0; if (ent.obj != 0) printf ("bad");
And: struct io_event ent = {}; ent.data = 0; if (ent.obj != 0) printf ("bad");
and that is even without speaking of complete variable elimination when the structure is not used, unknown pointer alignement when memset function is not inlined, or aliasing optimisation.
Etienne.
___________________________________________________________ Do You Yahoo!? -- Une adresse @yahoo.fr gratuite et en français ! Yahoo! Mail : http://fr.mail.yahoo.com - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |