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Tue, 19 Nov 2019 07:25:46 -0800 (PST) Date: Tue, 19 Nov 2019 17:25:43 +0200 From: Lorenzo Bianconi To: Jesper Dangaard Brouer Cc: mcroce@redhat.com, Lorenzo Bianconi , netdev@vger.kernel.org, davem@davemloft.net, ilias.apalodimas@linaro.org, jonathan.lemon@gmail.com Subject: Re: [PATCH v4 net-next 2/3] net: page_pool: add the possibility to sync DMA memory for device Message-ID: <20191119152543.GD3449@localhost.localdomain> References: <84b90677751f54c1c8d47f4036bce5999982379c.1574083275.git.lorenzo@kernel.org> <20191119122358.12276da4@carbon> <20191119121430.GA3449@localhost.localdomain> <20191119161332.56faa205@carbon> MIME-Version: 1.0 In-Reply-To: <20191119161332.56faa205@carbon> User-Agent: Mutt/1.12.1 (2019-06-15) X-Mimecast-Spam-Score: 0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="n2Pv11Ogg/Ox8ay5" Content-Disposition: inline Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org --n2Pv11Ogg/Ox8ay5 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable > On Tue, 19 Nov 2019 14:14:30 +0200 > Lorenzo Bianconi wrote: >=20 > > > On Mon, 18 Nov 2019 15:33:45 +0200 > > > Lorenzo Bianconi wrote: > > > =20 > > > > diff --git a/include/net/page_pool.h b/include/net/page_pool.h > > > > index 1121faa99c12..6f684c3a3434 100644 > > > > --- a/include/net/page_pool.h > > > > +++ b/include/net/page_pool.h > > > > @@ -34,8 +34,15 @@ > > > > #include > > > > #include > > > > =20 > > > > -#define PP_FLAG_DMA_MAP 1 /* Should page_pool do the DMA map/unmap= */ > > > > -#define PP_FLAG_ALL=09PP_FLAG_DMA_MAP > > > > +#define PP_FLAG_DMA_MAP=09=091 /* Should page_pool do the DMA map/= unmap */ > > > > +#define PP_FLAG_DMA_SYNC_DEV=092 /* if set all pages that the driv= er gets > > > > +=09=09=09=09 * from page_pool will be > > > > +=09=09=09=09 * DMA-synced-for-device according to the > > > > +=09=09=09=09 * length provided by the device driver. > > > > +=09=09=09=09 * Please note DMA-sync-for-CPU is still > > > > +=09=09=09=09 * device driver responsibility > > > > +=09=09=09=09 */ > > > > +#define PP_FLAG_ALL=09=09(PP_FLAG_DMA_MAP | PP_FLAG_DMA_SYNC_DEV) > > > > =20 > > > [...] > > >=20 > > > Can you please change this to use the BIT(X) api. > > >=20 > > > #include > > >=20 > > > #define PP_FLAG_DMA_MAP=09=09BIT(0) > > > #define PP_FLAG_DMA_SYNC_DEV=09BIT(1) =20 > >=20 > > Hi Jesper, > >=20 > > sure, will do in v5 > >=20 > > >=20 > > >=20 > > > =20 > > > > diff --git a/net/core/page_pool.c b/net/core/page_pool.c > > > > index dfc2501c35d9..4f9aed7bce5a 100644 > > > > --- a/net/core/page_pool.c > > > > +++ b/net/core/page_pool.c > > > > @@ -47,6 +47,13 @@ static int page_pool_init(struct page_pool *pool= , > > > > =09 (pool->p.dma_dir !=3D DMA_BIDIRECTIONAL)) > > > > =09=09return -EINVAL; > > > > =20 > > > > +=09/* In order to request DMA-sync-for-device the page needs to > > > > +=09 * be mapped > > > > +=09 */ > > > > +=09if ((pool->p.flags & PP_FLAG_DMA_SYNC_DEV) && > > > > +=09 !(pool->p.flags & PP_FLAG_DMA_MAP)) > > > > +=09=09return -EINVAL; > > > > + =20 > > >=20 > > > I like that you have moved this check to setup time. > > >=20 > > > There are two other parameters the DMA_SYNC_DEV depend on: > > >=20 > > > =09struct page_pool_params pp_params =3D { > > > =09=09.order =3D 0, > > > -=09=09.flags =3D PP_FLAG_DMA_MAP, > > > +=09=09.flags =3D PP_FLAG_DMA_MAP | PP_FLAG_DMA_SYNC_DEV, > > > =09=09.pool_size =3D size, > > > =09=09.nid =3D cpu_to_node(0), > > > =09=09.dev =3D pp->dev->dev.parent, > > > =09=09.dma_dir =3D xdp_prog ? DMA_BIDIRECTIONAL : DMA_FROM_DEVICE, > > > +=09=09.offset =3D pp->rx_offset_correction, > > > +=09=09.max_len =3D MVNETA_MAX_RX_BUF_SIZE, > > > =09}; > > >=20 > > > Can you add a check, that .max_len must not be zero. The reason is > > > that I can easily see people misconfiguring this. And the effect is > > > that the DMA-sync-for-device is essentially disabled, without user > > > realizing this. The not-realizing part is really bad, especially > > > because bugs that can occur from this are very rare and hard to catch= . =20 > >=20 > > I guess we need to check it just if we provide PP_FLAG_DMA_SYNC_DEV. > > Something like: > >=20 > > =09if (pool->p.flags & PP_FLAG_DMA_SYNC_DEV) { > > =09=09if (!(pool->p.flags & PP_FLAG_DMA_MAP)) > > =09=09=09return -EINVAL; > >=20 > > =09=09if (!pool->p.max_len) > > =09=09=09return -EINVAL; > >=09} >=20 > Yes, exactly. >=20 ack, I will add it to v5 > > >=20 > > > I'm up for discussing if there should be a similar check for .offset. > > > IMHO we should also check .offset is configured, and then be open to > > > remove this check once a driver user want to use offset=3D0. Does th= e > > > mvneta driver already have a use-case for this (in non-XDP mode)? =20 > >=20 > > With 'non-XDP mode' do you mean not loading a BPF program? If so yes, i= t used > > in __page_pool_alloc_pages_slow getting pages from page allocator. > > What would be a right min value for it? Just 0 or > > XDP_PACKET_HEADROOM/NET_SKB_PAD? I guess here it matters if a BPF progr= am is > > loaded or not. >=20 > I think you are saying, that we need to allow .offset=3D=3D0, because it = is > used by mvneta. Did I understand that correctly? I was just wondering what is the right value for the min offset, but rethin= king about it yes, there is a condition where mvneta is using offset set 0 (it = is the regression reported by Andrew, when mvneta is running on a hw bm device bu= t bm code is not compiled). Do you think we can skip this check for the moment u= ntil we fix XDP on that particular board? Regards, Lorenzo >=20 > --=20 > Best regards, > Jesper Dangaard Brouer > MSc.CS, Principal Kernel Engineer at Red Hat > LinkedIn: http://www.linkedin.com/in/brouer >=20 --n2Pv11Ogg/Ox8ay5 Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iHUEABYIAB0WIQTquNwa3Txd3rGGn7Y6cBh0uS2trAUCXdQJdAAKCRA6cBh0uS2t rKKJAQDCGL+xoR3gm83zinkQTttgBJVZJJcfP8cNt472bwkBZQD/XE5khppAvp0x 0t4U5DuMn1s09ZnUvk9hOCQy4z4mxgs= =YBCt -----END PGP SIGNATURE----- --n2Pv11Ogg/Ox8ay5--