Messages in this thread | | | From | Vinicius Costa Gomes <> | Subject | Re: [PATCH v2 net-next 7/9] net: netdevsim: mimic tc-taprio offload | Date | Tue, 01 Aug 2023 10:39:23 -0700 |
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Hi Vladimir,
Vladimir Oltean <vladimir.oltean@nxp.com> writes:
> On Wed, Jun 14, 2023 at 05:06:24PM -0700, Vinicius Costa Gomes wrote: >> > +static int nsim_setup_tc_taprio(struct net_device *dev, >> > + struct tc_taprio_qopt_offload *offload) >> > +{ >> > + int err = 0; >> > + >> > + switch (offload->cmd) { >> > + case TAPRIO_CMD_REPLACE: >> > + case TAPRIO_CMD_DESTROY: >> > + break; >> >> I was thinking about how useful would proper validation of the >> parameters be? Thinking that we could detect "driver API" breakages >> earlier, and we want it documented that the drivers should check for the >> things that it supports. >> >> Makes sense? > > Sorry, I lack imagination as to what the netdevsim driver may check for. > The taprio offload parameters should always be valid, properly speaking, > otherwise the Qdisc wouldn't be passing them on to the driver. At least > that would be the intention. The rest are hardware specific checks for > hardware specific limitations. Here there is no hardware. >
Trying to remember what was going through my mind when I said that.
What I seem to recall is something that would help us "keep honest": I was worrying about someone (perhaps myself ;-) sneaking a new feature in taprio and forgetting to update other drivers.
I thought that adding a check for the existing parameters would help detect those kind of things. If anything unknown was there in the offload struct, netdevsim would complain loudly.
Perhaps I was worrying too much. And the way to solve that is to keep active attention against that during review.
> The parameters passed to TAPRIO_CMD_REPLACE are: > > struct tc_mqprio_qopt_offload mqprio: > struct tc_mqprio_qopt qopt: validated by taprio_parse_mqprio_opt() for flags 0x2 > u16 mode: always set to TC_MQPRIO_MODE_DCB > u16 shaper: always set to TC_MQPRIO_SHAPER_DCB > u32 flags: always set to 0 > u64 min_rate[TC_QOPT_MAX_QUEUE]: always set to [0,] > u64 max_rate[TC_QOPT_MAX_QUEUE]: always set to [0,] > unsigned long preemptible_tcs: always set to 0, because ethtool_dev_mm_supported() returns false > > ktime_t base_time: any value is valid > > u64 cycle_time: any value is valid > > u64 cycle_time_extension: any value <= cycle_time is valid. According to 802.1Q > "Q.5 CycleTimeExtension variables", it's the maximum > amount by which the penultimate cycle can be extended > to avoid a very short cycle upon a ConfigChange event. > But if CycleTimeExtension is larger than one CycleTime, > then we're not even talking about the penultimate cycle > anymore, but about ones previous to that?! Maybe this > should be limited to 0 <= cycle_time_extension <= cycle_time > by taprio, certainly not by offloading drivers. >
Good point. I have to review 802.1Q, but from what I remember that sounds right, cycle_time_extension greater than cycle_time doesn't make much sense. Having a check for it in taprio itself sounds good.
> u32 max_sdu[TC_MAX_QUEUE]: limited to a value <= dev->max_mtu by taprio > > size_t num_entries: any value is valid > > struct tc_taprio_sched_entry entries[]: > u8 command: will be either one of: TC_TAPRIO_CMD_SET_GATES, TC_TAPRIO_CMD_SET_AND_HOLD > or TC_TAPRIO_CMD_SET_AND_RELEASE. However 802.1Q "Table 8-7—Gate operations" > says "If frame preemption is not supported or not enabled (preemptionActive is > FALSE), this operation behaves the same as SetGateStates.". So I > see no reason to enforce any restriction here either? > > u32 gate_mask: technically can have bits set, which correspond > to traffic classes larger than dev->num_tc. > Taprio can enforce this, so I wouldn't see > drivers beginning to feel paranoid about it. > Actually I had a patch about this: > https://patchwork.kernel.org/project/netdevbpf/patch/20230130173145.475943-15-vladimir.oltean@nxp.com/ > but I decided to drop it because I didn't have > any strong case for it. > u32 interval: any value is valid. If the sum of entry intervals > is less than the cycle_time, again that's taprio's > problem to check for, in its netlink attribute > validation method rather than offloading drivers. >
Thank you for the time it took to give this amount of detail.
Cheers, -- Vinicius
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