Messages in this thread | | | From | Howard Yen <> | Date | Thu, 8 Feb 2024 15:53:37 +0800 | Subject | Re: [PATCH v2] dma-coherent: add support for multi coherent rmems per dev |
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On Tue, Feb 6, 2024 at 11:43 PM Andy Shevchenko <andriy.shevchenko@linux.intel.com> wrote: > > On Mon, Feb 05, 2024 at 02:08:00PM +0200, Andy Shevchenko wrote: > > On Mon, Feb 05, 2024 at 07:23:00AM +0000, Howard Yen wrote: > > ... > > > > @@ -18,15 +18,9 @@ struct dma_coherent_mem { > > > unsigned long *bitmap; > > > spinlock_t spinlock; > > > bool use_dev_dma_pfn_offset; > > > + struct list_head node; > > > > Have you run `pahole`? Here I see wasted bytes for nothing. > > On top of that one may make container_of() to be no-op, by placing this member > to be the first one. But, double check this with bloat-o-meter (that it indeed > does better code generation) and on the other hand check if the current first > member is not performance critical and having additional pointer arithmetics is > okay. > > > > }; > > > -- > With Best Regards, > Andy Shevchenko > >
I'm trying to re-org the members as below
from ===>
struct dma_coherent_mem { void * virt_base; /* 0 8 */ dma_addr_t device_base; /* 8 8 */ unsigned long pfn_base; /* 16 8 */ int size; /* 24 4 */
/* XXX 4 bytes hole, try to pack */
unsigned long * bitmap; /* 32 8 */ spinlock_t spinlock; /* 40 4 */ bool use_dev_dma_pfn_offset; /* 44 1 */
/* XXX 3 bytes hole, try to pack */
struct list_head node; /* 48 16 */
/* size: 64, cachelines: 1, members: 8 */ /* sum members: 57, holes: 2, sum holes: 7 */ };
to ===>
struct dma_coherent_mem { struct list_head node; /* 0 16 */ void * virt_base; /* 16 8 */ dma_addr_t device_base; /* 24 8 */ unsigned long pfn_base; /* 32 8 */ int size; /* 40 4 */ spinlock_t spinlock; /* 44 4 */ unsigned long * bitmap; /* 48 8 */ bool use_dev_dma_pfn_offset; /* 56 1 */
/* size: 64, cachelines: 1, members: 8 */ /* padding: 7 */ };
Looks like there is about 7 bytes padding at the end of the structure. Should I add __attribute__((__packed__)) to not add the padding?
-- Regards,
Howard
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