Re: [Intel-gfx] Enabling sample_c optimization for Broadwell GPUs
Hi Rodrigo, Thank you very much for providing that information in a precise manner. Às 07:16 de 05/05/21, Rodrigo Vivi escreveu: Hi Andre, I'm not familiar with the sample c message optimization. Probably Ken can comment. However I could check the internal spec here and I saw this bit only exists with this meaning in Haswell. For all the other platforms, including Broadwell it got re-purposed with a different meaning and a programming note: "This bit should be programmed to zero (0h) at all times." Also, I could not find any workaround documented anywhere recommending this bit to be set. So, I would not recommend to use it in any product, even downstream. Regardless the state of sample c message optimization in later platforms. Thanks, Rodrigo. On Tue, May 04, 2021 at 08:07:14PM -0300, André Almeida wrote: Hi there, While browsing an old downstream kernel, I found a patch[0] that enables sample_c optimizations at Broadwell GPUs. The message from the upstream commit that enables it for Haswell[1] (and presumably where the code at[0] was copied from) states that "[..] later platforms remove this bit, and apparently always enable the optimization". Could you confirm that Broadwell and following architectures enable this optimization by default (and thus, patch[0] is a no-op), or should I upstream it? Thanks, André [0] https://github.com/ValveSoftware/steamos_kernel/commit/198990f13e1d9429864c177d9441a6559771c5e2 [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=944115934436b1ff6cf773a9e9123858ea9ef3da ___ Intel-gfx mailing list Intel-gfx@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/intel-gfx
Re: [Intel-gfx] Enabling sample_c optimization for Broadwell GPUs
Hello, Yes, that bit only exists on Haswell. On Haswell, sample_c operations were processed at 1 pixel/clock unless you set that bit, in which case they get processed at 4 pixels/clock. The downside is that it breaks some obscure media feature that apparently no one used. Broadwell and later alway process sample_c operations at the fast speed, and there is no bit to control it. I would say that downstream patch is incorrect. --Ken On Tuesday, May 4, 2021 4:07:14 PM PDT André Almeida wrote: > Hi there, > > While browsing an old downstream kernel, I found a patch[0] that enables > sample_c optimizations at Broadwell GPUs. The message from the upstream > commit that enables it for Haswell[1] (and presumably where the code > at[0] was copied from) states that "[..] later platforms remove this > bit, and apparently always enable the optimization". > > Could you confirm that Broadwell and following architectures enable this > optimization by default (and thus, patch[0] is a no-op), or should I > upstream it? > > Thanks, > André > > [0] > https://github.com/ValveSoftware/steamos_kernel/commit/198990f13e1d9429864c177d9441a6559771c5e2 > > [1] > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=944115934436b1ff6cf773a9e9123858ea9ef3da > signature.asc Description: This is a digitally signed message part. ___ Intel-gfx mailing list Intel-gfx@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/intel-gfx
Re: [Intel-gfx] Enabling sample_c optimization for Broadwell GPUs
Hi Andre, I'm not familiar with the sample c message optimization. Probably Ken can comment. However I could check the internal spec here and I saw this bit only exists with this meaning in Haswell. For all the other platforms, including Broadwell it got re-purposed with a different meaning and a programming note: "This bit should be programmed to zero (0h) at all times." Also, I could not find any workaround documented anywhere recommending this bit to be set. So, I would not recommend to use it in any product, even downstream. Regardless the state of sample c message optimization in later platforms. Thanks, Rodrigo. On Tue, May 04, 2021 at 08:07:14PM -0300, André Almeida wrote: > Hi there, > > While browsing an old downstream kernel, I found a patch[0] that enables > sample_c optimizations at Broadwell GPUs. The message from the upstream > commit that enables it for Haswell[1] (and presumably where the code at[0] > was copied from) states that "[..] later platforms remove this bit, and > apparently always enable the optimization". > > Could you confirm that Broadwell and following architectures enable this > optimization by default (and thus, patch[0] is a no-op), or should I > upstream it? > > Thanks, > André > > [0] > https://github.com/ValveSoftware/steamos_kernel/commit/198990f13e1d9429864c177d9441a6559771c5e2 > > [1] > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=944115934436b1ff6cf773a9e9123858ea9ef3da ___ Intel-gfx mailing list Intel-gfx@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/intel-gfx
