Messages in this thread | | | Date | Mon, 17 Dec 2007 09:03:37 -0800 | From | Arjan van de Ven <> | Subject | Re: [PATCH] Reduce overhead of CONFIG_TIMER_STATS |
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On Sun, 16 Dec 2007 19:29:44 -0200 Arnaldo Carvalho de Melo <acme@redhat.com> 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?
-- If you want to reach me at my work email, use arjan@linux.intel.com For development, discussion and tips for power savings, visit http://www.lesswatts.org
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