From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-172.mta0.migadu.com (out-172.mta0.migadu.com [91.218.175.172]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 95253401A21 for ; Thu, 26 Mar 2026 15:38:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774539524; cv=none; b=ZcLJD4MR8NunFXp6J0EcA20D3HBW3wOLLUsQIyb29B1KaWD6o9oukbIrdU6Lik49kFQxmkvUhFcEs4xxswZcshmkEHjgQtWvh2VgBIV75TLfZUsJIrT0R+B640o6q18RYfGuACnyAj2LTi287g8BhYEBwVLCxGtSzqzyQKk1qwY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774539524; c=relaxed/simple; bh=aEhVHb8Qplvx3MDDN4/y/lslZoMp99fsT9pBIUdUg1s=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=re5OoLDDHiNfnYaaZFuIoOWsTffwB5uYx9xvH9sTySjLXASPNRlvEDM5Xy93N0KOcOHWkzOZ19N/lUNjYFeBF7dp5vgj71kWrNOe7iyvv9JtTO7VFTE1sUKOqYP1mxAweTyTWBoCd5yitKZ71BjmzAj/5cVXFY01mCZZzJS5qDs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=NVh+vpmb; arc=none smtp.client-ip=91.218.175.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="NVh+vpmb" Message-ID: <9f6a4e9f-9f93-4ced-92de-8fdc6154c694@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1774539510; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=C1HBovL0iKKni3b5pUdpuk9v4ia3odEoFBnTktuY9oQ=; b=NVh+vpmbuQDOOJcwiZkJ1e+ML3EB3w0SQyx8QlDg2Xr65uXs/vBtWXXCebbMwh2mUbwRyC dgawcc8zWLwFqSro1X67SocFOBEk7Nv3Bc3jO2DPJavHQo+bdQYGdlkYfmM4nEw1aecuxW 2pI4NwGUHyrrxEZesORDRerYGCYmd5k= Date: Thu, 26 Mar 2026 11:38:24 -0400 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH net 2/2] net: xilinx: axienet: Fix BQL accounting for multi-BD TX packets To: "Gupta, Suraj" , "andrew+netdev@lunn.ch" , "davem@davemloft.net" , "edumazet@google.com" , "kuba@kernel.org" , "pabeni@redhat.com" , "Simek, Michal" , "Pandey, Radhey Shyam" , "horms@kernel.org" Cc: "netdev@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , "Katakam, Harini" References: <20260324145353.1899248-1-suraj.gupta2@amd.com> <20260324145353.1899248-3-suraj.gupta2@amd.com> Content-Language: en-US X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Sean Anderson In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT On 3/25/26 01:30, Gupta, Suraj wrote: > [Public] > >> -----Original Message----- >> From: Sean Anderson >> Sent: Tuesday, March 24, 2026 9:39 PM >> To: Gupta, Suraj ; andrew+netdev@lunn.ch; >> davem@davemloft.net; edumazet@google.com; kuba@kernel.org; >> pabeni@redhat.com; Simek, Michal ; Pandey, >> Radhey Shyam ; horms@kernel.org >> Cc: netdev@vger.kernel.org; linux-arm-kernel@lists.infradead.org; linux- >> kernel@vger.kernel.org; Katakam, Harini >> Subject: Re: [PATCH net 2/2] net: xilinx: axienet: Fix BQL accounting for multi-BD >> TX packets >> >> Caution: This message originated from an External Source. Use proper caution >> when opening attachments, clicking links, or responding. >> >> >> On 3/24/26 10:53, Suraj Gupta wrote: >> > When a TX packet spans multiple buffer descriptors (scatter-gather), >> > the per-BD byte count is accumulated into a local variable that resets >> > on each NAPI poll. If the BDs for a single packet complete across >> > different polls, the earlier bytes are lost and never credited to BQL. >> > This causes BQL to think bytes are permanently in-flight, eventually >> > stalling the TX queue. >> > >> > Fix this by replacing the local accumulator with a persistent counter >> > (tx_compl_bytes) that survives across polls and is reset only after >> > updating BQL and stats. >> >> Do we need this? Can't we just do something like >> > > Nope, the 'size' variable passed to axienet_free_tx_chain() is local > to axienet_tx_poll() and goes out of scope between different polls. > This means it can't track completion bytes across multiple NAPI polls. Yes, but that's fine since we only update completed bytes when we retire at least one packet: packets = axienet_free_tx_chain(lp, &size, budget); if (packets) { netdev_completed_queue(ndev, packets, size); u64_stats_update_begin(&lp->tx_stat_sync); u64_stats_add(&lp->tx_packets, packets); u64_stats_add(&lp->tx_bytes, size); u64_stats_update_end(&lp->tx_stat_sync); /* Matches barrier in axienet_start_xmit */ smp_mb(); if (((tail - ci) & (lp->rx_bd_num - 1)) >= MAX_SKB_FRAGS + 1) netif_wake_queue(ndev); } and this matches the value we use when enqueuing a packet tail_p = lp->tx_bd_p + sizeof(*lp->tx_bd_v) * (last_p - lp->tx_bd_v); smp_store_release(&lp->tx_bd_tail, new_tail_ptr); netdev_sent_queue(ndev, skb->len); > Regards, > Suraj > >> diff --git a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c >> b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c >> index 415e9bc252527..1ea8a6592bce1 100644 >> --- a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c >> +++ b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c >> @@ -768,6 +768,7 @@ static int axienet_free_tx_chain(struct axienet_local >> *lp, u32 *sizep, int budge >> if (cur_p->skb) { >> struct axienet_cb *cb = (void *)cur_p->skb->cb; >> >> + *sizep += skb->len; >> dma_unmap_sgtable(lp->dev, &cb->sgt, DMA_TO_DEVICE, 0); >> sg_free_table_chained(&cb->sgt, XAE_INLINE_SG_CNT); >> napi_consume_skb(cur_p->skb, budget); @@ -783,8 +784,6 @@ >> static int axienet_free_tx_chain(struct axienet_local *lp, u32 *sizep, int budge >> wmb(); >> cur_p->cntrl = 0; >> cur_p->status = 0; >> - >> - *sizep += status & XAXIDMA_BD_STS_ACTUAL_LEN_MASK; >> } >> >> smp_store_release(&lp->tx_bd_ci, (ci + i) & (lp->tx_bd_num - 1)); >> >> > Fixes: c900e49d58eb ("net: xilinx: axienet: Implement BQL") >> > Signed-off-by: Suraj Gupta >> > --- >> > drivers/net/ethernet/xilinx/xilinx_axienet.h | 3 +++ >> > .../net/ethernet/xilinx/xilinx_axienet_main.c | 20 +++++++++---------- >> > 2 files changed, 13 insertions(+), 10 deletions(-) >> > >> > diff --git a/drivers/net/ethernet/xilinx/xilinx_axienet.h >> > b/drivers/net/ethernet/xilinx/xilinx_axienet.h >> > index 602389843342..a4444c939451 100644 >> > --- a/drivers/net/ethernet/xilinx/xilinx_axienet.h >> > +++ b/drivers/net/ethernet/xilinx/xilinx_axienet.h >> > @@ -509,6 +509,8 @@ struct skbuf_dma_descriptor { >> > * complete. Only updated at runtime by TX NAPI poll. >> > * @tx_bd_tail: Stores the index of the next Tx buffer descriptor in the ring >> > * to be populated. >> > + * @tx_compl_bytes: Accumulates TX completion length until a full packet is >> > + * reported to the stack. >> > * @tx_packets: TX packet count for statistics >> > * @tx_bytes: TX byte count for statistics >> > * @tx_stat_sync: Synchronization object for TX stats @@ -592,6 >> > +594,7 @@ struct axienet_local { >> > u32 tx_bd_num; >> > u32 tx_bd_ci; >> > u32 tx_bd_tail; >> > + u32 tx_compl_bytes; >> > u64_stats_t tx_packets; >> > u64_stats_t tx_bytes; >> > struct u64_stats_sync tx_stat_sync; diff --git >> > a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c >> > b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c >> > index b06e4c37ff61..95bf61986cb7 100644 >> > --- a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c >> > +++ b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c >> > @@ -692,6 +692,8 @@ static void axienet_dma_stop(struct axienet_local >> *lp) >> > axienet_lock_mii(lp); >> > __axienet_device_reset(lp); >> > axienet_unlock_mii(lp); >> > + >> > + lp->tx_compl_bytes = 0; >> > } >> > >> > /** >> > @@ -770,8 +772,6 @@ static int axienet_device_reset(struct net_device >> *ndev) >> > * @first_bd: Index of first descriptor to clean up >> > * @nr_bds: Max number of descriptors to clean up >> > * @force: Whether to clean descriptors even if not complete >> > - * @sizep: Pointer to a u32 filled with the total sum of all bytes >> > - * in all cleaned-up descriptors. Ignored if NULL. >> > * @budget: NAPI budget (use 0 when not called from NAPI poll) >> > * >> > * Would either be called after a successful transmit operation, or >> > after @@ -780,7 +780,7 @@ static int axienet_device_reset(struct net_device >> *ndev) >> > * Return: The number of packets handled. >> > */ >> > static int axienet_free_tx_chain(struct axienet_local *lp, u32 first_bd, >> > - int nr_bds, bool force, u32 *sizep, int budget) >> > + int nr_bds, bool force, int budget) >> > { >> > struct axidma_bd *cur_p; >> > unsigned int status; >> > @@ -819,8 +819,8 @@ static int axienet_free_tx_chain(struct axienet_local >> *lp, u32 first_bd, >> > cur_p->cntrl = 0; >> > cur_p->status = 0; >> > >> > - if (sizep) >> > - *sizep += status & XAXIDMA_BD_STS_ACTUAL_LEN_MASK; >> > + if (!force) >> > + lp->tx_compl_bytes += status & >> > + XAXIDMA_BD_STS_ACTUAL_LEN_MASK; >> > } >> > >> > if (!force) { >> > @@ -999,18 +999,18 @@ static int axienet_tx_poll(struct napi_struct >> > *napi, int budget) { >> > struct axienet_local *lp = container_of(napi, struct axienet_local, napi_tx); >> > struct net_device *ndev = lp->ndev; >> > - u32 size = 0; >> > int packets; >> > >> > packets = axienet_free_tx_chain(lp, lp->tx_bd_ci, lp->tx_bd_num, false, >> > - &size, budget); >> > + budget); >> > >> > if (packets) { >> > - netdev_completed_queue(ndev, packets, size); >> > + netdev_completed_queue(ndev, packets, >> > + lp->tx_compl_bytes); >> > u64_stats_update_begin(&lp->tx_stat_sync); >> > u64_stats_add(&lp->tx_packets, packets); >> > - u64_stats_add(&lp->tx_bytes, size); >> > + u64_stats_add(&lp->tx_bytes, lp->tx_compl_bytes); >> > u64_stats_update_end(&lp->tx_stat_sync); >> > + lp->tx_compl_bytes = 0; >> > >> > /* Matches barrier in axienet_start_xmit */ >> > smp_mb(); >> > @@ -1115,7 +1115,7 @@ axienet_start_xmit(struct sk_buff *skb, struct >> net_device *ndev) >> > netdev_err(ndev, "TX DMA mapping error\n"); >> > ndev->stats.tx_dropped++; >> > axienet_free_tx_chain(lp, orig_tail_ptr, ii + 1, >> > - true, NULL, 0); >> > + true, 0); >> > dev_kfree_skb_any(skb); >> > return NETDEV_TX_OK; >> > }