From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx3-rdu2.redhat.com ([66.187.233.73]:46892 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1755426AbeCSNMZ (ORCPT ); Mon, 19 Mar 2018 09:12:25 -0400 Date: Mon, 19 Mar 2018 14:12:17 +0100 From: Jesper Dangaard Brouer To: Tariq Toukan Cc: netdev@vger.kernel.org, =?UTF-8?B?QmrDtnJuVMO2cGVs?= , magnus.karlsson@intel.com, eugenia@mellanox.com, Jason Wang , John Fastabend , Eran Ben Elisha , Saeed Mahameed , galp@mellanox.com, Daniel Borkmann , Alexei Starovoitov , brouer@redhat.com Subject: Re: [bpf-next V3 PATCH 13/15] mlx5: use page_pool for xdp_return_frame call Message-ID: <20180319141217.416d269a@redhat.com> In-Reply-To: <6e62fa6a-53c7-57a9-0493-3a48d832b479@mellanox.com> References: <152062887576.27458.8590966896888512270.stgit@firesoul> <152062896782.27458.5542026179434739900.stgit@firesoul> <247192bd-761e-426c-c462-59efe3b7ca97@mellanox.com> <22866952-6bdf-2529-91a1-fb31bd2f2c2d@mellanox.com> <6e62fa6a-53c7-57a9-0493-3a48d832b479@mellanox.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: netdev-owner@vger.kernel.org List-ID: On Mon, 12 Mar 2018 15:20:06 +0200 Tariq Toukan wrote: > On 12/03/2018 12:16 PM, Tariq Toukan wrote: > > > > On 12/03/2018 12:08 PM, Tariq Toukan wrote: > >> > >> On 09/03/2018 10:56 PM, Jesper Dangaard Brouer wrote: > >>> This patch shows how it is possible to have both the driver local page > >>> cache, which uses elevated refcnt for "catching"/avoiding SKB > >>> put_page.  And at the same time, have pages getting returned to the > >>> page_pool from ndp_xdp_xmit DMA completion. > >>> [...] > >>> > >>> Before this patch: single flow performance was 6Mpps, and if I started > >>> two flows the collective performance drop to 4Mpps, because we hit the > >>> page allocator lock (further negative scaling occurs). > >>> > >>> V2: Adjustments requested by Tariq > >>>   - Changed page_pool_create return codes not return NULL, only > >>>     ERR_PTR, as this simplifies err handling in drivers. > >>>   - Save a branch in mlx5e_page_release > >>>   - Correct page_pool size calc for MLX5_WQ_TYPE_LINKED_LIST_STRIDING_RQ > >>> > >>> Signed-off-by: Jesper Dangaard Brouer > >>> --- > >> > >> I am running perf tests with your series. I sense a drastic > >> degradation in regular TCP flows, I'm double checking the numbers now... > > > > Well, there's a huge performance degradation indeed, whenever the > > regular flows (non-XDP) use the new page pool. Cannot merge before > > fixing this. > > > > If I disable the local page-cache, numbers get as low as 100's of Mbps > > in TCP stream tests. > > It seems that the page-pool doesn't fit as a general fallback (when page > in local rx cache is busy), as the refcnt is elevated/changing: I see the issue. I have to go over the details in the driver, but I think it should be sufficient to remove the WARN(). When the page_pool was integrated with the MM-layer, being invoked from the put_page() call itself, this would indicate a likely API misuse. But now, with the page refcnt based recycle tricks, it is the norm (for non-XDP) that put_page is called without the knowledge of page_pool. > [ 7343.086102] ------------[ cut here ]------------ > [ 7343.086103] __page_pool_put_page() violating page_pool invariance refcnt:0 > [ 7343.086114] WARNING: CPU: 1 PID: 17 at net/core/page_pool.c:291 __page_pool_put_page+0x7c/0xa0 Here page_pool actually catch the page refcnt race correctly, and does the proper handling of returning it to the page allocator (via __put_page). I do notice (in the page_pool code) that in case page_pool handles DMA mapping (which isn't the case, yet), that I'm missing a DMA unmap release in the code. -- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat LinkedIn: http://www.linkedin.com/in/brouer