lkml.org 
[lkml]   [2024]   [Feb]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [PATCH v2] dma-coherent: add support for multi coherent rmems per dev
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

\
 
 \ /
  Last update: 2024-05-27 14:54    [W:0.230 / U:0.056 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site