On Sun, Feb 16, 2025 at 10:36 PM Willem de Bruijn <willemdebruijn.kernel@xxxxxxxxx> wrote: > > Jason Xing wrote: > > On Sun, Feb 16, 2025 at 6:58 AM Martin KaFai Lau <martin.lau@xxxxxxxxx> wrote: > > > > > > On 2/15/25 2:23 PM, Jason Xing wrote: > > > > On Sun, Feb 16, 2025 at 2:08 AM Willem de Bruijn > > > > <willemdebruijn.kernel@xxxxxxxxx> wrote: > > > >> > > > >> Jason Xing wrote: > > > >>> On Sat, Feb 15, 2025 at 11:06 PM Willem de Bruijn > > > >>> <willemdebruijn.kernel@xxxxxxxxx> wrote: > > > >>>> > > > >>>> Jason Xing wrote: > > > >>>>> Support hw SCM_TSTAMP_SND case for bpf timestamping. > > > >>>>> > > > >>>>> Add a new sock_ops callback, BPF_SOCK_OPS_TS_HW_OPT_CB. This > > > >>>>> callback will occur at the same timestamping point as the user > > > >>>>> space's hardware SCM_TSTAMP_SND. The BPF program can use it to > > > >>>>> get the same SCM_TSTAMP_SND timestamp without modifying the > > > >>>>> user-space application. > > > >>>>> > > > >>>>> To avoid increasing the code complexity, replace SKBTX_HW_TSTAMP > > > >>>>> with SKBTX_HW_TSTAMP_NOBPF instead of changing numerous callers > > > >>>>> from driver side using SKBTX_HW_TSTAMP. The new definition of > > > >>>>> SKBTX_HW_TSTAMP means the combination tests of socket timestamping > > > >>>>> and bpf timestamping. After this patch, drivers can work under the > > > >>>>> bpf timestamping. > > > >>>>> > > > >>>>> Considering some drivers doesn't assign the skb with hardware > > > >>>>> timestamp, > > > >>>> > > > >>>> This is not for a real technical limitation, like the skb perhaps > > > >>>> being cloned or shared? > > > >>> > > > >>> Agreed on this point. I'm kind of familiar with I40E, so I dare to say > > > >>> the reason why it doesn't assign the hwtstamp is because the skb will > > > >>> soon be destroyed, that is to say, it's pointless to assign the > > > >>> timestamp. > > > >> > > > >> Makes sense. > > > >> > > > >> But that does not ensure that the skb is exclusively owned. Nor that > > > >> the same is true for all drivers using this API (which is not small, > > > >> but small enough to manually review if need be). > > > >> > > > >> The first two examples I happened to look at, i40e and bnx2x, both use > > > >> skb_get() to get a non-exclusive skb reference for their ptp_tx_skb. > > > > > > I think the existing __skb_tstamp_tx() function is also assigning to > > > skb_hwtstamps(skb). The skb may be cloned from the orig_skb first, but they > > > still share the same shinfo. My understanding is that this patch is assigning to > > > the shinfo earlier, so it should not have changed the driver's expectation on > > > the skb_hwtstamps(skb) after calling __skb_tstamp_tx(). If there are drivers > > > assuming exclusive access to the skb_hwtstamps(skb), probably it is something > > > that needs to be addressed regardless and should not be the common case? > > > > Right, it's also what I was trying to say but missed. Thanks for the > > supplementary info:) > > That existing behavior looks dodgy then, too. > > I don't have time to look into it deeply right now. But it seems to go > back all the way to the introduction of hw timestamping in commit > ac45f602ee3d in 2009. Right. And hardware timestamping has been used for many years, I presume. > > I can see how it works in that nothing else holding a clone will > likely have a reason to touch those fields. But that does not make it > correct. > > Your point that the new code is no worse than today probably is true. Right. > But when we spot something we prefer to fix it probably. Will need a > deeper look.. Got it. I added it to my to-do list. If you don't mind, I plan to take a deep look in March and then get back to you because recently I'm occupied by many things. I need to study some of the drivers that don't use skb_get() there. Thanks, Jason
