Em Mon, Dec 17, 2007 at 09:03:37AM -0800, Arjan van de Ven escreveu:
> On Sun, 16 Dec 2007 19:29:44 -0200
> Arnaldo Carvalho de Melo <[email protected]> wrote:
>
> > Hi,
> > While looking at the pahole output for struct timer_list on
> > recent kernels I noticed that there is a 4 bytes padding on struct
> > timer_list that gets propagated to many structs on 64 bits
> > architectures:
> >
> > [acme@doppio linux-2.6]$ pahole -C timer_list /tmp/tcp.o.before
> > struct timer_list {
> > struct list_head entry; /* 0 16 */
> > long unsigned int expires; /* 16 8 */
> > void (*function)(long unsigned int); /*
> > 24 8 */ long unsigned int data; /* 32 8 */
> > struct tvec_t_base_s *base; /* 40 8 */
> > void * start_site; /* 48 8 */
> > char start_comm[16]; /* 56 16 */
> > /* --- cacheline 1 boundary (64 bytes) was 8 bytes ago --- */
> > int start_pid; /* 72 4 */
> >
> > /* size: 80, cachelines: 2 */
> > /* padding: 4 */
> > /* last cacheline: 16 bytes */
> > };
> > [acme@doppio linux-2.6]$
> >
> > So the attached patch reduces the 4 bytes hole overhead of
> > CONFIG_TIMER_STATS on 64bit architectures by shrinking the field for
> > the process name by 4 bytes.
> >
> > Statistically this doesn't affects that many process names as
> > most are less than 12 bytes. As CONFIG_TIMER_STATS is enabled at least
> > on fedora kernels I think that we can, with this patch, still reap the
> > benefits of powertopping.
>
> I'm still worried that this means that PowerTOP will end up displaying shortened names..
> it's already sometimes tricky to know who's guilty at 16... at 12 I fear it just gets worse.
> Isn't there some other reorder that you can do to still get rid of the hole?
Nope. As shown above there is no other hole that we can conbine with the
4 bytes padding on struct timer_list.
<brainfarting>
What we could do, perhaps, would be to struct start_comm to be a pointer
and store the strings in a list, refcounted, so instead of 16 or 12
bytes we would use 8, but would incur in some CPU overhead definetely
bigger than a simple memcpy, but that would reduce even further the
memory footprint.
But the hole would still be there, as it would be sizeof(void *) +
sizeof(start_pid) :-)
</>
- Arnaldo
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
