On 04/01/2011 19:59, Roman Divacky wrote:
hi,
clang (svn version) has ability to detect unnecessary padding in structures.
I ran this on kernel build on i386 (stripped GENERIC) and amd64 (full GENERIC),
preprocessed this and posted on web.
The lists contain the file of the definition, name of the structure, size of
the unnecessary padding and reason for the alignment. The last field is
how many times this was hit during the build of the kernel.
It looks like "padding... to alignment boundary" means "because of
struct {...} __aligned(CACHE_LINE_SIZE)" and such, and we cannot run
away from those - maybe you should filter those results out?
The lists are sorted by the size of the padding.
Examples (i386):
dev/usb/controller/ohci.h:64:8: 2 times
padding size of 'struct ohci_hcca' with 120 bytes to alignment boundary
sys/pcpu.h:156:8: 58 times
padding size of 'struct pcpu' with 108 bytes to alignment boundary
sys/pcpu.h:199:2: 58 times
padding struct 'struct pcpu' with 84 bytes to align 'pc_monitorbuf'
dev/usb/controller/ehci.h:170:8: 1 times
padding size of 'struct ehci_qtd' with 58 bytes to alignment boundary
kern/sched_ule.c:206:8: 1 times
padding size of 'struct tdq' with 41 bytes to alignment boundary
Examples(amd64):
net/flowtable.c:179:11: 1 times
padding struct 'struct flowtable' with 124 bytes to align 'ft_udp_idle'
dev/usb/controller/ohci.h:64:8: 2 times
padding size of 'struct ohci_hcca' with 120 bytes to alignment boundary
net/flowtable.c:160:8: 1 times
padding size of 'struct flowtable' with 108 bytes to alignment boundary
vm/uma_int.h:184:8: 6 times
padding size of 'struct uma_cache' with 96 bytes to alignment boundary
vm/uma_int.h:338:19: 5 times
padding struct 'struct uma_zone' with 92 bytes to align 'uz_cpu'
net/flowtable.c:149:8: 1 times
padding size of 'struct flowtable_stats' with 64 bytes to alignment
boundary
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