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Date: Sat, 2 Mar 2024 04:04:08 +0000
From: "Song, Yoong Siang" <yoong.siang.song@...el.com>
To: John Fastabend <john.fastabend@...il.com>, "Brandeburg, Jesse"
<jesse.brandeburg@...el.com>, "Nguyen, Anthony L"
<anthony.l.nguyen@...el.com>, "David S . Miller" <davem@...emloft.net>, "Eric
Dumazet" <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni
<pabeni@...hat.com>, Richard Cochran <richardcochran@...il.com>, "Alexei
Starovoitov" <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>,
"Jesper Dangaard Brouer" <hawk@...nel.org>, Stanislav Fomichev
<sdf@...gle.com>, "Gomes, Vinicius" <vinicius.gomes@...el.com>, "Bezdeka,
Florian" <florian.bezdeka@...mens.com>, Andrii Nakryiko <andrii@...nel.org>,
"Eduard Zingerman" <eddyz87@...il.com>, Mykola Lysenko <mykolal@...com>,
"Martin KaFai Lau" <martin.lau@...ux.dev>, Song Liu <song@...nel.org>,
Yonghong Song <yonghong.song@...ux.dev>, KP Singh <kpsingh@...nel.org>, Hao
Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>, Shuah Khan
<shuah@...nel.org>
CC: "intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>,
"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"bpf@...r.kernel.org" <bpf@...r.kernel.org>,
"linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
"xdp-hints@...-project.net" <xdp-hints@...-project.net>
Subject: RE: [PATCH iwl-next,v2 2/2] igc: Add Tx hardware timestamp request
for AF_XDP zero-copy packet
On Saturday, March 2, 2024 1:55 AM, John Fastabend <john.fastabend@...il.com> wrote:
>Song Yoong Siang wrote:
>> This patch adds support to per-packet Tx hardware timestamp request to
>> AF_XDP zero-copy packet via XDP Tx metadata framework. Please note that
>> user needs to enable Tx HW timestamp capability via igc_ioctl() with
>> SIOCSHWTSTAMP cmd before sending xsk Tx hardware timestamp request.
>>
>> Same as implementation in RX timestamp XDP hints kfunc metadata, Timer 0
>> (adjustable clock) is used in xsk Tx hardware timestamp. i225/i226 have
>> four sets of timestamping registers. Both *skb and *xsk_tx_buffer pointers
>> are used to indicate whether the timestamping register is already occupied.
>>
>> Furthermore, a boolean variable named xsk_pending_ts is used to hold the
>> transmit completion until the tx hardware timestamp is ready. This is
>> because, for i225/i226, the timestamp notification event comes some time
>> after the transmit completion event. The driver will retrigger hardware irq
>> to clean the packet after retrieve the tx hardware timestamp.
>>
>> Besides, xsk_meta is added into struct igc_tx_timestamp_request as a hook
>> to the metadata location of the transmit packet. When the Tx timestamp
>> interrupt is fired, the interrupt handler will copy the value of Tx hwts
>> into metadata location via xsk_tx_metadata_complete().
>>
>> Co-developed-by: Lai Peter Jun Ann <jun.ann.lai@...el.com>
>> Signed-off-by: Lai Peter Jun Ann <jun.ann.lai@...el.com>
>> Signed-off-by: Song Yoong Siang <yoong.siang.song@...el.com>
>> ---
>
>[...]
>
>>
>> +static void igc_xsk_request_timestamp(void *_priv)
>> +{
>> + struct igc_metadata_request *meta_req = _priv;
>> + struct igc_ring *tx_ring = meta_req->tx_ring;
>> + struct igc_tx_timestamp_request *tstamp;
>> + u32 tx_flags = IGC_TX_FLAGS_TSTAMP;
>> + struct igc_adapter *adapter;
>> + unsigned long lock_flags;
>> + bool found = false;
>> + int i;
>> +
>> + if (test_bit(IGC_RING_FLAG_TX_HWTSTAMP, &tx_ring->flags)) {
>> + adapter = netdev_priv(tx_ring->netdev);
>> +
>> + spin_lock_irqsave(&adapter->ptp_tx_lock, lock_flags);
>> +
>> + /* Search for available tstamp regs */
>> + for (i = 0; i < IGC_MAX_TX_TSTAMP_REGS; i++) {
>> + tstamp = &adapter->tx_tstamp[i];
>> +
>> + if (tstamp->skb)
>> + continue;
>> +
>> + found = true;
>> + break;
>
>Not how I would have written this loop construct seems a bit odd
>to default break but it works.
Hi John,
First of all, thank you for reviewing the patch.
I agree that we can make the loop better.
How about I change the loop to below:
for (i = 0; i < IGC_MAX_TX_TSTAMP_REGS; i++) {
tstamp = &adapter->tx_tstamp[i];
if (!tstamp->skb) {
found = true;
break;
}
}
>
>> + }
>> +
>> + /* Return if no available tstamp regs */
>> + if (!found) {
>> + adapter->tx_hwtstamp_skipped++;
>> + spin_unlock_irqrestore(&adapter->ptp_tx_lock,
>> + lock_flags);
>> + return;
>> + }
>
>[...]
>
>>
>> +static void igc_ptp_free_tx_buffer(struct igc_adapter *adapter,
>> + struct igc_tx_timestamp_request *tstamp)
>> +{
>> + if (tstamp->buffer_type == IGC_TX_BUFFER_TYPE_XSK) {
>> + /* Release the transmit completion */
>> + tstamp->xsk_tx_buffer->xsk_pending_ts = false;
>> + tstamp->xsk_tx_buffer = NULL;
>> + tstamp->buffer_type = 0;
>> +
>> + /* Trigger txrx interrupt for transmit completion */
>> + igc_xsk_wakeup(adapter->netdev, tstamp->xsk_queue_index, 0);
>
>Just curious because I didn't find it. Fairly sure I just need to look more,
>but don't you want to still 'tstamp->skb = NULL' in this path somewhere?
>It looks like triggering the tx interrupt again with buffer_type == 0 wouldn't
>do the null.
>
>I suspect I just missed it.
Since the timestamp register will only be used by either skb or xsk,
So we make tstamp->xsk_tx_buffer and tstamp->skb as union,
Then based on tstamp->buffer_type to decide whether
tstamp->xsk_tx_buffer or tstamp->skb should be used.
My thought is, by setting tstamp->xsk_tx_buffer=NULL,
tstamp->skb will become NULL as well, and vice versa.
Thanks & Regards
Siang
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