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Tue, 08 Sep 2020 08:12:16 -0700 (PDT) Subject: Re: [PATCH bpf-next 4/4] ixgbe, xsk: use XSK_NAPI_WEIGHT as NAPI poll budget To: =?UTF-8?B?QmrDtnJuIFTDtnBlbA==?= , Eric Dumazet , =?UTF-8?B?QmrDtnJuIFTDtnBlbA==?= , ast@kernel.org, daniel@iogearbox.net, netdev@vger.kernel.org, bpf@vger.kernel.org Cc: magnus.karlsson@intel.com, kuba@kernel.org, intel-wired-lan@lists.osuosl.org References: <20200907150217.30888-1-bjorn.topel@gmail.com> <20200907150217.30888-5-bjorn.topel@gmail.com> <6bbf1793-d2be-b724-eec4-65546d4cbc9c@gmail.com> From: Eric Dumazet Message-ID: Date: Tue, 8 Sep 2020 17:12:10 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On 9/8/20 1:49 PM, Björn Töpel wrote: > On 2020-09-08 11:45, Eric Dumazet wrote: >> >> >> On 9/7/20 5:02 PM, Björn Töpel wrote: >>> From: Björn Töpel >>> >>> Start using XSK_NAPI_WEIGHT as NAPI poll budget for the AF_XDP Rx >>> zero-copy path. >>> >>> Signed-off-by: Björn Töpel >>> --- >>>   drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c | 2 +- >>>   1 file changed, 1 insertion(+), 1 deletion(-) >>> >>> diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c >>> index 3771857cf887..f32c1ba0d237 100644 >>> --- a/drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c >>> +++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c >>> @@ -239,7 +239,7 @@ int ixgbe_clean_rx_irq_zc(struct ixgbe_q_vector *q_vector, >>>       bool failure = false; >>>       struct sk_buff *skb; >>>   -    while (likely(total_rx_packets < budget)) { >>> +    while (likely(total_rx_packets < XSK_NAPI_WEIGHT)) { >>>           union ixgbe_adv_rx_desc *rx_desc; >>>           struct ixgbe_rx_buffer *bi; >>>           unsigned int size >> >> This is a violation of NAPI API. IXGBE is already diverging a bit from best practices. >> > > Thanks for having a look, Eric! By diverging from best practices, do > you mean that multiple queues share one NAPI context, and the budget > is split over the queues (say, 4 queues, 64/4 per queue), or that Tx > simply ignores the budget? Or both? For instance, having ixgbe_poll() doing : return min(work_done, budget - 1); is quite interesting. It could hide bugs like : I got a budget of 4, and processed 9999 packets because my maths have a bug, but make sure to pretend we processed 3 packets... > >> There are reasons we want to control the budget from callers, >> if you want bigger budget just increase it instead of using your own ? >> >> I would rather use a generic patch. >> > > Hmm, so a configurable NAPI budget for, say, the AF_XDP enabled > queues/NAPIs? Am I reading that correct? (Note that this is *only* for > the AF_XDP enabled queues.) > > I'll try to rework this to something more palatable. > > > Thanks, > Björn > >