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SubjectRe: [PATCH] radeon: Shrink radeon_ring_write()
De-duplicating the error message is probably a good idea, but are the 
remaining code changes really necessary for the size reduction?

Regards,
Christian.

On 18.05.2015 19:59, Denys Vlasenko wrote:
> Inlined radeon_ring_write() has 729 callers, which amounts to about 50000
> bytes of code. however, deinlining it is probably too much
> of a performance impact.
>
> This patch shrinks slow path a bit and optimizes fast path.
> Comparison of generated machine code is below:
>
> old___________________________________ new____________________________
> 55 push %rbp 55 push %rbp
> 4889e5 mov %rsp,%rbp ff4f38 decl 0x38(%rdi)
> 4154 push %r12 4889e5 mov %rsp,%rbp
> 4189f4 mov %esi,%r12d 4154 push %r12
> 53 push %rbx 4189f4 mov %esi,%r12d
> 837f3800 cmpl $0x0,0x38(%rdi) 53 push %rbx
> 4889fb mov %rdi,%rbx 4889fb mov %rdi,%rbx
> 7f0e jg <.Lbl> 7905 jns <.Lbl>
> 48c7c78f51a785 mov $message,%rdi
> 31c0 xor %eax,%eax
> e89306f9ff call <drm_err> e8cbffffff call <radeon_ring_overflow>
> .Lbl:
> 8b4328 mov 0x28(%rbx),%eax 8b5328 mov 0x28(%rbx),%edx
> 488b5308 mov 0x8(%rbx),%rdx 488b4308 mov 0x8(%rbx),%rax
> 89c1 mov %eax,%ecx 488d0490 lea (%rax,%rdx,4),%rax
> ffc0 inc %eax
> 488d148a lea (%rdx,%rcx,4),%rdx 448920 mov %r12d,(%rax)
> 448922 mov %r12d,(%rdx) 8b4328 mov 0x28(%rbx),%eax
> 234354 and 0x54(%rbx),%eax ff4b34 decl 0x34(%rbx)
> ff4b38 decl 0x38(%rbx) ffc0 inc %eax
> ff4b34 decl 0x34(%rbx) 234354 and 0x54(%rbx),%eax
> 894328 mov %eax,0x28(%rbx) 894328 mov %eax,0x28(%rbx)
> 5b pop %rbx 5b pop %rbx
> 415c pop %r12 415c pop %r12
> 5d pop %rbp 5d pop %rbp
>
> This shaves off more than 10 kbytes of code off the kernel:
>
> text data bss dec hex filename
> 85657104 22294872 20627456 128579432 7a9f768 vmlinux.before
> 85646544 22294872 20627456 128568872 7a9ce28 vmlinux
>
> Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
> Cc: Christian König <christian.koenig@amd.com>
> Cc: Alex Deucher <alexander.deucher@amd.com>
> Cc: linux-kernel@vger.kernel.org
> ---
> drivers/gpu/drm/radeon/radeon.h | 11 +++++------
> drivers/gpu/drm/radeon/radeon_ring.c | 5 +++++
> 2 files changed, 10 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/radeon/radeon.h b/drivers/gpu/drm/radeon/radeon.h
> index bb6b25c..9106873 100644
> --- a/drivers/gpu/drm/radeon/radeon.h
> +++ b/drivers/gpu/drm/radeon/radeon.h
> @@ -2658,14 +2658,13 @@ void radeon_atombios_fini(struct radeon_device *rdev);
> *
> * Write a value to the requested ring buffer (all asics).
> */
> +void radeon_ring_overflow(void);
> static inline void radeon_ring_write(struct radeon_ring *ring, uint32_t v)
> {
> - if (ring->count_dw <= 0)
> - DRM_ERROR("radeon: writing more dwords to the ring than expected!\n");
> -
> - ring->ring[ring->wptr++] = v;
> - ring->wptr &= ring->ptr_mask;
> - ring->count_dw--;
> + if (--ring->count_dw < 0)
> + radeon_ring_overflow();
> + ring->ring[ring->wptr] = v;
> + ring->wptr = (ring->wptr + 1) & ring->ptr_mask;
> ring->ring_free_dw--;
> }
>
> diff --git a/drivers/gpu/drm/radeon/radeon_ring.c b/drivers/gpu/drm/radeon/radeon_ring.c
> index 2456f69..8204c23 100644
> --- a/drivers/gpu/drm/radeon/radeon_ring.c
> +++ b/drivers/gpu/drm/radeon/radeon_ring.c
> @@ -126,6 +126,11 @@ int radeon_ring_alloc(struct radeon_device *rdev, struct radeon_ring *ring, unsi
> return 0;
> }
>
> +void radeon_ring_overflow(void)
> +{
> + DRM_ERROR("radeon: writing more dwords to the ring than expected!\n");
> +}
> +
> /**
> * radeon_ring_lock - lock the ring and allocate space on it
> *



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