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 C913FC27C4F for ; Tue, 18 Jun 2024 18:08:15 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 86DCF10E217; Tue, 18 Jun 2024 18:08:15 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (2048-bit key; unprotected) header.d=intel.com header.i=@intel.com header.b="id8lfHwO"; dkim-atps=neutral Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.15]) by gabe.freedesktop.org (Postfix) with ESMTPS id A7F6610E22C for ; Tue, 18 Jun 2024 18:08:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1718734093; x=1750270093; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=naauMmX5Zx4JhaqBamV5Wxif5sMIFv5ev2QcpiDoB1c=; b=id8lfHwO1K4U6Kgj0lfhmIalECphc6vQTmoMSgcheZMmfa564WW+S74d kql5zDi2zUypQVc+LjBdovnrgV6Yzp22wfS+XBPrWt/ugfcMmzFSWskHl 6FyX29iu5GFzWd1TxQEV/5RGDYuSmzYqhTH0tLMTLmaASnQvDX12m+G3E mzD7I3soqmv2/ogqNLh1ocjw/0kilxsTEJ2Pn7ofTdUBobbYpoJftjKZG UgLX0duE/pMxJcJLV0goBa8no16JuJD/Z4kmGVaeOdxhda3ib3Vf94X18 ZgU95HJmH/bZ1smVQA4eGZJ4BvcsDDm5hOi+77+JIqX/IkdFR7lf2ClsB Q==; X-CSE-ConnectionGUID: Tu+ka7MJROC4MGihs3SYGw== X-CSE-MsgGUID: FNlUFaYcQBuTOUtDwhs/ew== X-IronPort-AV: E=McAfee;i="6700,10204,11107"; a="15783921" X-IronPort-AV: E=Sophos;i="6.08,247,1712646000"; d="scan'208";a="15783921" Received: from fmviesa006.fm.intel.com ([10.60.135.146]) by fmvoesa109.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 18 Jun 2024 11:08:12 -0700 X-CSE-ConnectionGUID: WWrSl5zHR/uzjUbgAAMEPg== X-CSE-MsgGUID: ZDn+0ABpQnWIxJ+ps0A2+A== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.08,247,1712646000"; d="scan'208";a="41495984" Received: from irvmail002.ir.intel.com ([10.43.11.120]) by fmviesa006.fm.intel.com with ESMTP; 18 Jun 2024 11:08:09 -0700 Received: from [10.245.82.128] (mwajdecz-MOBL.ger.corp.intel.com [10.245.82.128]) by irvmail002.ir.intel.com (Postfix) with ESMTP id DAF5334308; Tue, 18 Jun 2024 19:08:06 +0100 (IST) Message-ID: Date: Tue, 18 Jun 2024 20:08:05 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC 0/3] FW guard class To: Matthew Brost , Lucas De Marchi Cc: Rodrigo Vivi , =?UTF-8?Q?Thomas_Hellstr=C3=B6m?= , intel-xe@lists.freedesktop.org References: <20240617143430.641-1-michal.wajdeczko@intel.com> Content-Language: en-US From: Michal Wajdeczko In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-BeenThere: intel-xe@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel Xe graphics driver List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: intel-xe-bounces@lists.freedesktop.org Sender: "Intel-xe" On 18.06.2024 03:16, Matthew Brost wrote: > On Mon, Jun 17, 2024 at 07:54:41PM -0500, Lucas De Marchi wrote: >> On Mon, Jun 17, 2024 at 11:30:41PM GMT, Matthew Brost wrote: >>> On Mon, Jun 17, 2024 at 09:24:42PM +0200, Michal Wajdeczko wrote: >>>> >>>> >>>> On 17.06.2024 20:00, Rodrigo Vivi wrote: >>>>> On Mon, Jun 17, 2024 at 05:24:24PM +0000, Matthew Brost wrote: >>>>>> On Mon, Jun 17, 2024 at 04:34:27PM +0200, Michal Wajdeczko wrote: >>>>>>> There is support for 'classes' with constructor and destructor >>>>>>> semantics that can be used for any scope-based resource management, >>>>>>> like device force-wake management. >>>>>>> >>>>>>> Add necessary definitions explicitly, since existing macros from >>>>>>> linux/cleanup.h can't deal with our specific requirements yet. >>>>>>> >>>>>>> This should allow us to use: >>>>>>> >>>>>>> scoped_guard(xe_fw, fw, XE_FW_GT) >>>>>>> foo(); >>>>>>> or >>>>>>> CLASS(xe_fw, var)(fw, XE_FW_GT); >>>>>>> >>>>>>> without any concern of leaking the force-wake references. >>>>>>> >>>>>>> Note: this is preliminary code as right now it's unclear how to >>>>>>> correctly handle errors from the force-wake functions. >>>>>>> >>>>>> >>>>>> I'm personally don't like this at all. IMO it obfuscate the code with >>>>>> little real benefit. This is just an opinion though, others opinions may >>>>>> differ from mine. >>>> >>>> except that is more robust than hand-crafted code that is error prone, >>>> like this snippet from wedged_mode_set(): >>>> >>>> xe_pm_runtime_get(xe); >>>> for_each_gt(gt, xe, id) { >>>> ret = xe_guc_ads(...); >>>> if (ret) { >>>> xe_gt_err(gt, "..."); >>>> return -EIO; >>>> } >>>> } >>>> xe_pm_runtime_put(xe); >>>> >>>> and thanks to PM guard class we could avoid such mistakes for free: >>>> >>>> scoped_guard(xe_pm, xe) { >>>> for_each_gt(gt, xe, id) { >>>> ret = xe_guc_ads(...); >>>> if (ret) { >>>> xe_gt_err(gt, "..."); >>>> return -EIO; >>> >>> Just responding with a question here - haven't looked at the rest of the >>> comments. >>> >>> How is this not still a bug? Looking at scoped_guard, it appears to be a >>> magic macro for loop which acquires / releases a lock or in your >>> purposed case a PM or FW ref. Doesn't the 'return -EIO' skip the release >>> step? I see coding patterns like above in the kernel [1] so I do assume >> >> with __attribute__((cleanup)), the compiler guarantees that >> it's executed when the variable goes out of scope. What you are probably >> missing is the use of CLASS() declaring a variable inside the for, which >> uses attribute cleanup: >> >> for (CLASS(_name, scope)(args), >> ... >> >> GCC's doc: >> >> https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html >> >> The cleanup attribute runs a function when the variable goes out >> of scope. This attribute can only be applied to auto function >> scope variables; it may not be applied to parameters or >> variables with static storage duration. The function must take >> one parameter, a pointer to a type compatible with the variable. >> The return value of the function (if any) is ignored. >> >> When multiple variables in the same scope have cleanup >> attributes, at exit from the scope their associated cleanup >> functions are run in reverse order of definition (last defined, >> first cleanup). >> >> If -fexceptions is enabled, then cleanup_function is run during >> the stack unwinding that happens during the processing of the >> exception. Note that the cleanup attribute does not allow the >> exception to be caught, only to perform an action. It is >> undefined what happens if cleanup_function does not return >> normally. >> >> This was only possible with the recent change in the kernel raising >> the minimum C std to gnu11 (uapi is still c90 for compatibility): >> >> commit e8c07082a810fbb9db303a2b66b66b8d7e588b53 >> Author: Arnd Bergmann >> Date: Tue Mar 8 22:56:14 2022 +0100 >> >> Kbuild: move to -std=gnu11 >> >> During a patch discussion, Linus brought up the option of changing >> the C standard version from gnu89 to gnu99, which allows using variable >> declaration inside of a for() loop. While the C99, C11 and later standards >> introduce many other features, most of these are already available in >> gnu89 as GNU extensions as well. >> > > Thanks for the reference, will checkout. > >>> this works, just confused how it works. >>> >>> With that, any code which isn't easily understandable IMO is a negative >>> ROI as it just creates confusion in the long / makes problems harder to >>> understand. Again this is just my opinion. >> >> I think that is mainly about getting used to the pattern. I think we > > Agree once pattern is understood, fairly easy change. > >> just have to be careful not to overshoot on trying to use everywhere. > > Agree about overshooting. I think we agree we want to use cleanup.h > semantics in Xe we should start by converting kernel core components > (spin locks, mutexes, rwsem, kfree, etc...) to use these semantics > before adding our own ones. Also with this, I think if we use cleanup.h > semantics, we use these semantics everywhere we can (e.g. directly > grabbing a spin lock is akin to open coding and not allowed). > > Once we convert Xe core componets to use these semantics then we start > adding Xe specific ones. > > Thoughts? IMO if we decide to promote new cleanup mechanism for core primitives like mutex/spinlocks then we should already have wrappers for Xe specific stuff like PM and FW handy to avoid mixing patterns and allow use them together if applicable/desired: scoped_guard(xe_pm, xe) scoped_guard(xe_fw, fw, XE_FW_GT) scoped_guard(spinlock, &lock) foo(); and even if we just allow, without immediate enforcing this new cleanup mechanism, then it still could be beneficial to introduce PM/FW support to start closing any gaps we may have in any of these areas and to do that in small steps whenever we make changes around problematic code > >> For example, I don't know why there's already a second use in a separate >> thread when we are still discussing it on this one. >> >> A very positive thing is that this is not xe's own invention and comes > > I agree, it is core fairly new core thing which seems to widely > endorsed which is a positive. > >> from core kernel, maybe from the hottest path that is the scheduling and >> locking. So I very much disagree with arguments raised here about >> a) this is an alien thing and b) performance will be severely impacted >> >> I've used __attribute__((cleanup)) in several userspace projects in the >> past and it does help avoiding problems on the error path that is >> usually not very well tested (and xe's track record on error path is not > > For sure our error paths are not great but it isn't like this solves our > of those problems magically. > >> very good either: those were the main issues being submitted in drm-xe-fixes >> for the last release). So if we have a way to improve (and that I've already seen >> being used successfully), I prefer failing on trying than on repeating >> the same mistakes. In kmod my only regret is that I didn't start it >> earlier, during the bootstrap of the project. > > This merged a little over a year, so quite new. Xe is still fairly small > and I don't think it would be to painful to switch over to these > semantics. If we want do this, I'd say we do this asap. thanks for reconsidering your initial strong position > > Matt > >> >> >> Lucas De Marchi >> >> >>> >>> Matt >>> >>> [1] https://elixir.bootlin.com/linux/latest/source/drivers/iio/imu/bmi323/bmi323_core.c#L1544 >>> >>>> } >>>> } >>>> } >>>> >>>>> >>>>> Well, on the positive side, it is not adding a driver only thing like >>>>> i915's with_runtime_pm() macro. >>>>> >>>>> But I'm also not sure if I like the overall idea anyway: >>>>> >>>>> - I don't like adding C++isms in a pure C code. Specially something not >>>>> so standard and common that will decrease the ramp-up time for newcomers. >>>> >>>> does it mean that the use of other guard patterns seen elsewhere in the >>>> tree is now prohibited on the Xe driver ? like: >>>> >>>> scoped_guard(mutex, &lock) >>>> foo(); >>>> >>>> scoped_guard(spinlock, &lock) >>>> foo(); >>>> ... >>>> >>>>> - It looks like and extra overhead on the object creation destruction. >>>> >>>> from cleanup.h doc is sounds there is none: >>>> >>>> "And through the magic of value-propagation and dead-code-elimination, >>>> it eliminates the actual cleanup call and compiles into:" >>>> >>>> >>>>> - It looks not flexible for handling different cases... like forcewake for >>>>> instance where we might want to ignore the ack timeout in some cases. >>>> >>>> there is scoped_cond_guard() that likely will be able to deal with it, >>>> but I guess we first need to cleanup existing force_wake api as expected >>>> flow is not clear and there are different approaches in the driver how >>>> to deal with errors >>>> >>>>> >>>>>> >>>>>> Matt >>>>>> >>>>>>> Cc: Rodrigo Vivi >>>>>>> Cc: Lucas De Marchi >>>>>>> >>>>>>> Michal Wajdeczko (3): >>>>>>> drm/xe: Introduce force-wake guard class >>>>>>> drm/xe: Use new FW guard in xe_mocs.c >>>>>>> drm/xe: Use new FW guard in xe_pat.c >>>>>>> >>>>>>> drivers/gpu/drm/xe/xe_force_wake.h | 48 +++++++++++++++++++ >>>>>>> drivers/gpu/drm/xe/xe_force_wake_types.h | 12 +++++ >>>>>>> drivers/gpu/drm/xe/xe_mocs.c | 12 +---- >>>>>>> drivers/gpu/drm/xe/xe_pat.c | 60 ++++++++---------------- >>>>>>> 4 files changed, 82 insertions(+), 50 deletions(-) >>>>>>> >>>>>>> -- >>>>>>> 2.43.0 >>>>>>>