Messages in this thread | | | Subject | Re: [PATCH] slub: reduce total stack usage of slab_err & object_err | From | Matt Mackall <> | Date | Tue, 30 Sep 2008 12:37:25 -0500 |
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On Tue, 2008-09-30 at 17:20 +0100, Richard Kennedy wrote: > Yes, using vprintk is better but you still have this path : > ( with your patch applied) > > object_err -> slab_bug(208) -> printk(216) > instead of > object_err -> slab_bug_message(8) -> printk(216) > > unfortunately the overhead for having var_args is pretty big, at least > on x86_64. I haven't measured it on 32 bit yet.
That's fascinating. I tried a simple test case in userspace:
#include <stdarg.h> #include <stdio.h>
void p(char *fmt, ...) { va_list args;
va_start(args, fmt); vprintf(fmt, args); va_end(args); }
On 32-bit, I'm seeing 32 bytes of stack vs 216 on 64-bit. Disassembly suggests it's connected to va_list fiddling with XMM registers, which seems quite odd.
-- Mathematics is the supreme nostalgia of our time.
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