From mboxrd@z Thu Jan 1 00:00:00 1970 From: Thomas Hellstrom Subject: Re: [PATCH 0/1][RFC] drm/ttm Improved io_mem_reserve / io_mem_free_calling Date: Thu, 11 Nov 2010 17:50:28 +0100 Message-ID: <4CDC1ED4.4070903@vmware.com> References: <1289464917-25085-1-git-send-email-thellstrom@vmware.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: Received: from smtp-outbound-2.vmware.com (smtp-outbound-2.vmware.com [65.115.85.73]) by gabe.freedesktop.org (Postfix) with ESMTP id 8BD239EF20 for ; Thu, 11 Nov 2010 08:50:41 -0800 (PST) In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dri-devel-bounces+sf-dri-devel=m.gmane.org@lists.freedesktop.org Errors-To: dri-devel-bounces+sf-dri-devel=m.gmane.org@lists.freedesktop.org To: Jerome Glisse Cc: "airlied@redhat.com" , "dri-devel@lists.freedesktop.org" List-Id: dri-devel@lists.freedesktop.org On 11/11/2010 04:27 PM, Jerome Glisse wrote: > On Thu, Nov 11, 2010 at 3:41 AM, Thomas Hellstrom wrote: > >> The following patch is really intended for the next merge window. >> >> RFC: >> 1) Are there any implementations of driver::io_mem_reserve today that can't use >> the fastpath? >> 2) Can we put an atomic requirement on driver::io_mem_reserve / >> driver::io_mem_free? >> >> The patch improves on the io_mem_reserve / io_mem_free calling sequences by >> introducing a fastpath and an optional eviction mechanism. >> >> The fastpath is enabled by default and is switched off by the driver setting >> struct ttm_mem_type_manager::io_reserve_fastpath to false on mem type init. >> With the fastpath no locking occurs, and io_mem_free is never called. >> I'm not sure if there are any implementations today that could not use the >> fastpath. >> >> As mentioned in the patch, if the fastpath is disabled, calls to >> io_mem_reserve and io_mem_free are exactly balanced, and refcounted within >> struct ttm_mem_reg so that io_mem_reserve should never be called recursively >> for the same struct ttm_mem_reg. >> Locking is required to make sure that ptes are never present on when the >> underlying memory region is not reserved. Currently I'm using >> man::io_reserve_mutex for this. Can we use a spinlock? That would require >> io_mem_reserve and io_mem_free to be atomic. >> >> Optionally, there is an eviction mechanism that is activated by setting >> struct ttm_mem_type_manager::use_io_reserve_lru to true when initialized. >> If the eviction mechanism is activated, and io_mem_reserve returns -EAGAIN, >> it will attempt to kill user-space mappings to free up reserved regions. >> Kernel mappings (ttm_bo_kmap) are not affected. >> >> > Radeon can use fast path, i think nouveau can too. I am not sure we > can consider io_mem_reserve as atomic. Use case i fear is GPU with > remappable apperture i don't know what kind of code we would need for > that and it might sleep. Thought my first guess is that it likely can > be done atomicly. > In that case, I think I will change it to a spinlock, with a code comment that it can be changed to a mutex later if it turns out to be very hard / impossible to implement atomic operations. Another possible concern is the execution of umap_mapping_range() that may in some cases be long. Perhaps too long to use a spinlock. > Quick review of the patch looks good, i will try to take a closer look latter. > > Cheers, > Jerome Glisse > Great. Thanks, Thomas