From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2C4D860A2605 for ; Tue, 27 Oct 2026 12:42:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=intel.com header.i=@intel.com header.a=rsa-sha256 header.s=Intel header.b=EofktGYX Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id E1AC110E40B; Tue, 27 Oct 2026 12:42:24 +0000 (UTC) Received: from mgamail.intel.com (mgamail.intel.com [198.175.65.16]) by gabe.freedesktop.org (Postfix) with ESMTPS id 1CD9A10E40B for ; Tue, 27 Oct 2026 12:42:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1793104939; x=1824640939; h=message-id:date:mime-version:subject:from:to:cc: references:in-reply-to:content-transfer-encoding; bh=NMEa5vWU4ZlNJLykssghl9O3s6Ml6pgdhRGqV7VPbts=; b=EofktGYXXZJqhklz0WdIAtoHHhE+ceb17RN3HF0G98bNdt0bXPhQaA8S RVe21M1VpOr/jh7rVrYJCKpsKlMe7tEakjLi3GXJRqSr+2aUHABKzvGjQ B7Ju6GOEQtV8sO42o5a/UDLnPZX8zEkF8SRlPhcbez8ViVTHiA0za+DfE eJXRndLM44lOMsI7+63OkikLnHACbFXYJAe90BrKyilG9tE/fqbun2r// +/HmQ1ZqM34W6uvqDgS7vViUN755l0yGxIzxG+OBEzmE4qPPyRgA3csjP 9obz5J6R6abVLTI8juxcJvvQiu3Oq2LQHweimuqLl+Dy3N7zbdfsgJ6Hv g==; X-CSE-ConnectionGUID: 2Vmk2BsVSWyxbsXldP0q4g== X-CSE-MsgGUID: mRI1HDDAQN2GVNVZaqwdzw== X-IronPort-AV: E=McAfee;i="6800,10657,11947"; a="1790041" X-IronPort-AV: E=Sophos;i="6.27,181,1787036400"; d="scan'208";a="1790041" Received: from orviesa004.jf.intel.com ([10.64.159.144]) by orvoesa108.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 27 Oct 2026 05:42:18 -0700 X-CSE-ConnectionGUID: dSeO7xJfQMOp0jxELMjmdw== X-CSE-MsgGUID: QgWc/OjfSbaLYded+0PQLw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.27,181,1787036400"; d="scan'208";a="4556012" Received: from abityuts-desk1.ger.corp.intel.com (HELO [10.245.244.18]) ([10.245.244.18]) by smtpauth.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 27 Oct 2026 05:42:16 -0700 Message-ID: Date: Tue, 27 Oct 2026 12:42:13 +0000 X-Archived-By: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/2] drm/xe/sa: make suballocator waits uninterruptible From: Matthew Auld To: =?UTF-8?Q?Thomas_Hellstr=C3=B6m?= , intel-xe@lists.freedesktop.org Cc: Matthew Brost , stable@vger.kernel.org References: <20261022174058.226432-4-matthew.auld@intel.com> <20261022174058.226432-5-matthew.auld@intel.com> <45831f6088cde19e2885cbbde52574da8a595e18.camel@linux.intel.com> <3c39fc90-de66-44a6-936e-06a69219f7af@intel.com> Content-Language: en-GB In-Reply-To: <3c39fc90-de66-44a6-936e-06a69219f7af@intel.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-BeenThere: intel-xe@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel Xe graphics driver List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "Intel-xe" X-Spam-Status: No, score=-17.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=4.0.1 X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On 23/10/2026 10:32, Matthew Auld wrote: > Hi, > > On 22/10/2026 19:29, Thomas Hellström wrote: >> Hi, Matt >> >> On Thu, 2026-10-22 at 18:41 +0100, Matthew Auld wrote: >>> Large BO clears and copies in xe_migrate_clear() and >>> xe_migrate_copy() >>> are split into multiple passes, each needing a batchbuffer from the >>> fixed size kernel bb pool. Once the pool fills up, __xe_sa_bo_new() >>> waits interruptibly for space, so a pending signal (e.g. Xorg's 5ms >>> SIGALRM smart-scheduler timer) makes it fail mid-loop with - >>> ERESTARTSYS. >>> The partial progress is then thrown away and the restarted ioctl >>> starts >>> again from byte 0, including the memory allocation, which can >>> livelock >>> if the signal arrives faster than the whole operation completes. In >>> the >>> shrinker path the same error also aborts the shrinker walk, even >>> though >>> ctx->interruptible is false. >>> >>> Being interruptible here doesn't seem to buy much anyway: on error >>> the loop already waits uninterruptibly for all submitted passes >>> before >>> returning. So just make the suballocator waits uninterruptible, >>> matching >>> amdgpu and radeon. The other users (page reclaim from a kworker, and >>> the >>> GuC buffer cache) shouldn't really see any meaningful change. >> >> This is a deviation from the "make all waits possible interruptible". >> One might argue that user-space that interrupts kernel work with a 5ms >> time only to restart it again and again is not well-behaving and >> continously shoots itself in the foot. > > Maybe. This is the xserver, so I assume this is very old and not some > new thing. I feel like even in this situation the kernel should be able > to make some forward progress in the ioctl. > >> >> Given our pipelining abilities, isn't there a risk that we delay signal >> delivery with up to 10s? > > At least for the copy/clear, it looks like there is already an > uninterruptible wait on the err path if fence != NULL, which we trigger > on a signal. > >> >> In the worst case, is there a way we can periodically at least check >> for pending signals or perhaps increase the sa bo size so that it >> doesn't block on a single large buffer? > > Other idea is to expose the intr, and then maybe plumb down the ctx- > >interruptible somehow, which would then cover the shrinker case and > maybe other places like that which explicitly asked for that? For the > clear case (gem_create) maybe we check if the fence != NULL first and > then set intr accordingly? If we have a pending signal it would bail if > we have not started GPU clearing yet, but if we have started then we try > to finish? The error path will currently do an uninterruptible wait > anyway, and that one could be a lot worse for a big buffer, since it > drains ALL prior jobs, instead of just waiting for the oldest bb. And > here it might be that we got right to the tail end of the clears but we > got a signal, so we throw away all of that work. > > Increasing the sa bo is also an option (maybe both). Although I guess > there will likely still be something too big, and I guess we might still > see issues if the pool is still busy with other pending work? Some more thoughts. Since Matt nuked the vm_bind GPU path, I don't think there is much contention on the reserved bcs any more since there is just one migrate queue (?), so maybe we can also: 1. Bump the VRAM clear + identity path. 8M is maybe very pessimistic now? Maybe we could push a lot more work per MEM_SET + page mode here? This could also give more perf, with a lot fewer jobs for 1G+ buffers. I have seen llama.py with 5G+ gemma model use 1G+ buffer on my BMG, for example. 2. Maybe also pack more work per-bb, at least for identity? Each new bb eats up a bunch of padding for pre-fetch etc. > >> >> /Thomas >> >>> >>> Assisted-by: LLM >>> Link: https://gitlab.freedesktop.org/drm/xe/kernel/-/work_items/9644 >>> Fixes: dd08ebf6c352 ("drm/xe: Introduce a new DRM driver for Intel >>> GPUs") >>> Signed-off-by: Matthew Auld >>> Cc: Thomas Hellström >>> Cc: Matthew Brost >>> Cc: # v6.12+ >>> --- >>>   drivers/gpu/drm/xe/xe_sa.c | 5 +++-- >>>   1 file changed, 3 insertions(+), 2 deletions(-) >>> >>> diff --git a/drivers/gpu/drm/xe/xe_sa.c b/drivers/gpu/drm/xe/xe_sa.c >>> index f32045f40b7a..d9c2b28b08c2 100644 >>> --- a/drivers/gpu/drm/xe/xe_sa.c >>> +++ b/drivers/gpu/drm/xe/xe_sa.c >>> @@ -165,7 +165,8 @@ void xe_sa_bo_sync_shadow(struct drm_suballoc >>> *sa_bo) >>>    * @size: number of bytes we want to suballocate >>>    * @gfp: gfp flags used for memory allocation. Typically GFP_KERNEL. >>>    * >>> - * Try to make a suballocation of size @size. >>> + * Try to make a suballocation of size @size. Any waits for space >>> are >>> + * uninterruptible. >>>    * >>>    * Return: a &drm_suballoc, or an ERR_PTR. >>>    */ >>> @@ -178,7 +179,7 @@ struct drm_suballoc *__xe_sa_bo_new(struct >>> xe_sa_manager *sa_manager, u32 size, >>>       if (size > sa_manager->base.size) >>>           return ERR_PTR(-ENOBUFS); >>> -    return drm_suballoc_new(&sa_manager->base, size, gfp, true, >>> 0); >>> +    return drm_suballoc_new(&sa_manager->base, size, gfp, false, >>> 0); >>>   } >>>   /** >