Messages in this thread | | | Date | Thu, 8 Feb 2024 12:56:27 +0200 | From | Andy Shevchenko <> | Subject | Re: [PATCH v2] dma-coherent: add support for multi coherent rmems per dev |
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On Thu, Feb 08, 2024 at 03:53:37PM +0800, Howard Yen wrote: > 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. > > > > > > }; > > 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 */
Which seems better that above, right?
> }; > > Looks like there is about 7 bytes padding at the end of the structure. > Should I add __attribute__((__packed__)) to not add the padding?
No, __packed is about alignment, may give you much worse code generation. With list_head member first you might get better code from the original, check it with bloat-o-meter.
-- With Best Regards, Andy Shevchenko
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