netdev - Re: [PATCH net-next] xsk: introduce xsk_dma

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <ZEFlG9rINkutmpCT@infradead.org>
Date:   Thu, 20 Apr 2023 09:15:23 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Alexander Lobakin <aleksander.lobakin@...el.com>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Jakub Kicinski <kuba@...nel.org>,
        Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, netdev@...r.kernel.org,
        Björn Töpel <bjorn@...nel.org>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>, bpf@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Guenter Roeck <linux@...ck-us.net>,
        Gerd Hoffmann <kraxel@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jens Axboe <axboe@...nel.dk>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH net-next] xsk: introduce xsk_dma_ops

On Thu, Apr 20, 2023 at 03:59:39PM +0200, Alexander Lobakin wrote:
> Hmm, currently almost all Ethernet drivers map Rx pages once and then
> just recycle them, keeping the original DMA mapping. Which means pages
> can have the same first mapping for very long time, often even for the
> lifetime of the struct device. Same for XDP sockets, the lifetime of DMA
> mappings equals the lifetime of sockets.
> Does it mean we'd better review that approach and try switching to
> dma_alloc_*() family (non-coherent/caching in our case)?

Yes, exactly.  dma_alloc_noncoherent can be used exactly as alloc_pages
+ dma_map_* by the driver (including the dma_sync_* calls on reuse), but
has a huge number of advantages.

> Also, I remember I tried to do that for one my driver, but the thing
> that all those functions zero the whole page(s) before returning them to
> the driver ruins the performance -- we don't need to zero buffers for
> receiving packets and spend a ton of cycles on it (esp. in cases when 4k
> gets zeroed each time, but your main body of traffic is 64-byte frames).

Hmm, the single zeroing when doing the initial allocation shows up
in these profiles?