From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 9A8F0C433F5 for ; Wed, 6 Apr 2022 14:02:46 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id E7E2110E14F; Wed, 6 Apr 2022 14:02:45 +0000 (UTC) Received: from mga14.intel.com (mga14.intel.com [192.55.52.115]) by gabe.freedesktop.org (Postfix) with ESMTPS id 5738F10E1A2 for ; Wed, 6 Apr 2022 14:02:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1649253765; x=1680789765; h=date:from:to:cc:subject:message-id:references: mime-version:content-transfer-encoding:in-reply-to; bh=jAmLjQkOvXD1rNwNJOJHKBrmM/qqOc0FqPka05yFiRg=; b=nzAEfI6zAEZayzoWK4wdV1H6F5grTWFubbodoG8xvjvdGRdBsMetq/kj RQKREOCL1kFdbiWb1pjVEKEhiusnTJuhjyOepE+vOm4rBZJetNHcnY7Iu SqAoBQaXxTCsNRZAZS+dIf8FmByfcFRyMwAISbeynlNRlWjlrwFrcFuUE 6C9ulRN9avGS7kB37/R9nMR0Z9uaI/+TkUUA5VQbbB9Lq9UmIK0dFd61T 63gTa+DG861cWguTp5DSdOAmSjCl9HXnaoFJaD/8VTcW07wC8SC7m6Xvm /wy/6884MCVplb7+l6GPaAmTi4Mv6leyycJJjSgHV8ZUaZk0TvfEttgbh w==; X-IronPort-AV: E=McAfee;i="6200,9189,10309"; a="261226440" X-IronPort-AV: E=Sophos;i="5.90,239,1643702400"; d="scan'208";a="261226440" Received: from orsmga008.jf.intel.com ([10.7.209.65]) by fmsmga103.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 06 Apr 2022 07:01:43 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.90,239,1643702400"; d="scan'208";a="570528808" Received: from stinkpipe.fi.intel.com (HELO stinkbox) ([10.237.72.51]) by orsmga008.jf.intel.com with SMTP; 06 Apr 2022 07:01:40 -0700 Received: by stinkbox (sSMTP sendmail emulation); Wed, 06 Apr 2022 17:01:39 +0300 Date: Wed, 6 Apr 2022 17:01:39 +0300 From: Ville =?iso-8859-1?Q?Syrj=E4l=E4?= To: "Lisovskiy, Stanislav" Message-ID: References: <20220404134918.729038-1-vinod.govindapillai@intel.com> <20220406134526.GA22124@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20220406134526.GA22124@intel.com> X-Patchwork-Hint: comment Subject: Re: [Intel-gfx] [PATCH] drm/i915: program wm blocks to at least blocks required per line X-BeenThere: intel-gfx@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel graphics driver community testing & development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: intel-gfx@lists.freedesktop.org Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" On Wed, Apr 06, 2022 at 04:45:26PM +0300, Lisovskiy, Stanislav wrote: > On Wed, Apr 06, 2022 at 03:48:02PM +0300, Ville Syrjälä wrote: > > On Mon, Apr 04, 2022 at 04:49:18PM +0300, Vinod Govindapillai wrote: > > > In configurations with single DRAM channel, for usecases like > > > 4K 60 Hz, FIFO underruns are observed quite frequently. Looks > > > like the wm0 watermark values need to bumped up because the wm0 > > > memory latency calculations are probably not taking the DRAM > > > channel's impact into account. > > > > > > As per the Bspec 49325, if the ddb allocation can hold at least > > > one plane_blocks_per_line we should have selected method2. > > > Assuming that modern HW versions have enough dbuf to hold > > > at least one line, set the wm blocks to equivalent to blocks > > > per line. > > > > > > cc: Ville Syrjälä > > > cc: Stanislav Lisovskiy > > > > > > Signed-off-by: Vinod Govindapillai > > > --- > > > drivers/gpu/drm/i915/intel_pm.c | 19 ++++++++++++++++++- > > > 1 file changed, 18 insertions(+), 1 deletion(-) > > > > > > diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c > > > index 8824f269e5f5..ae28a8c63ca4 100644 > > > --- a/drivers/gpu/drm/i915/intel_pm.c > > > +++ b/drivers/gpu/drm/i915/intel_pm.c > > > @@ -5474,7 +5474,24 @@ static void skl_compute_plane_wm(const struct intel_crtc_state *crtc_state, > > > } > > > } > > > > > > - blocks = fixed16_to_u32_round_up(selected_result) + 1; > > > + /* > > > + * Lets have blocks at minimum equivalent to plane_blocks_per_line > > > + * as there will be at minimum one line for lines configuration. > > > + * > > > + * As per the Bspec 49325, if the ddb allocation can hold at least > > > + * one plane_blocks_per_line, we should have selected method2 in > > > + * the above logic. Assuming that modern versions have enough dbuf > > > + * and method2 guarantees blocks equivalent to at least 1 line, > > > + * select the blocks as plane_blocks_per_line. > > > + * > > > + * TODO: Revisit the logic when we have better understanding on DRAM > > > + * channels' impact on the level 0 memory latency and the relevant > > > + * wm calculations. > > > + */ > > > + blocks = skl_wm_has_lines(dev_priv, level) ? > > > + max_t(u32, fixed16_to_u32_round_up(selected_result) + 1, > > > + fixed16_to_u32_round_up(wp->plane_blocks_per_line)) : > > > + fixed16_to_u32_round_up(selected_result) + 1; > > > > That's looks rather convoluted. > > > > blocks = fixed16_to_u32_round_up(selected_result) + 1; > > + /* blah */ > > + if (has_lines) > > + blocks = max(blocks, fixed16_to_u32_round_up(wp->plane_blocks_per_line)); > > We probably need to do similar refactoring in the whole function ;-) > > > > > Also since Art said nothing like this should actually be needed > > I think the comment should make it a bit more clear that this > > is just a hack to work around the underruns with some single > > memory channel configurations. > > It is actually not quite a hack, because we are missing that condition > implementation from BSpec 49325, which instructs us to select method2 > when ddb blocks allocation is known and that ratio is >= 1. The ddb allocation is not yet known, so we're implementing the algorithm 100% correctly. And this patch does not implement that misisng part anyway. > > Mean this one: > > "If ('plane buffer allocation' is known and (plane buffer allocation / plane blocks per line) >=1) > Selected Result Blocks = Method 2" > > Stan > > > > > > > > lines = div_round_up_fixed16(selected_result, > > > wp->plane_blocks_per_line); > > > > > > -- > > > 2.25.1 > > > > -- > > Ville Syrjälä > > Intel -- Ville Syrjälä Intel