Re: [PATCH net-next v6 0/4] net/sched: retpoline wrappers for tc

Re: [PATCH net-next v6 0/4] net/sched: retpoline wrappers for tc

[Rudi Heitbaum]

Hi Pedro,

Compiling kernel 6.2-rc1 fails on x86_64 when CONFIG_NET_CLS or
CONFIG_NET_CLS_ACT is not set, when CONFIG_RETPOLINE=y is set.

Does tc_wrapper RETPOLINE need a dependency on NET_CLS/NET_CLS_ACT
to be added? Or a default?

net/sched/sch_api.c: In function 'pktsched_init':
net/sched/sch_api.c:2306:9: error: implicit declaration of function
'tc_wrapper_init' [-Werror=implicit-function-declaration]
 2306 |         tc_wrapper_init();
      |         ^~~~~~~~~~~~~~~
cc1: some warnings being treated as errors
make[3]: *** [scripts/Makefile.build:252: net/sched/sch_api.o] Error 1
make[2]: *** [scripts/Makefile.build:504: net/sched] Error 2
make[1]: *** [scripts/Makefile.build:504: net] Error 2

below is the relevent lines from the .config file.

$ grep -e RETPOLINE -e NET_CLS projects/Generic/linux/linux.x86_64.conf 
CONFIG_RETPOLINE=y
# CONFIG_NET_CLS_BASIC is not set
# CONFIG_NET_CLS_TCINDEX is not set
# CONFIG_NET_CLS_ROUTE4 is not set
# CONFIG_NET_CLS_FW is not set
# CONFIG_NET_CLS_U32 is not set
# CONFIG_NET_CLS_RSVP is not set
# CONFIG_NET_CLS_RSVP6 is not set
# CONFIG_NET_CLS_FLOW is not set
# CONFIG_NET_CLS_CGROUP is not set
# CONFIG_NET_CLS_BPF is not set
# CONFIG_NET_CLS_FLOWER is not set
# CONFIG_NET_CLS_MATCHALL is not set
# CONFIG_NET_CLS_ACT is not set

On Tue, Dec 06, 2022 at 10:55:09AM -0300, Pedro Tammela wrote:
> In tc all qdics, classifiers and actions can be compiled as modules.
> This results today in indirect calls in all transitions in the tc hierarchy.
> Due to CONFIG_RETPOLINE, CPUs with mitigations=on might pay an extra cost on
> indirect calls. For newer Intel cpus with IBRS the extra cost is
> nonexistent, but AMD Zen cpus and older x86 cpus still go through the
> retpoline thunk.
> 
> Known built-in symbols can be optimized into direct calls, thus
> avoiding the retpoline thunk. So far, tc has not been leveraging this
> build information and leaving out a performance optimization for some
> CPUs. In this series we wire up 'tcf_classify()' and 'tcf_action_exec()'
> with direct calls when known modules are compiled as built-in as an
> opt-in optimization.
> 
> We measured these changes in one AMD Zen 4 cpu (Retpoline), one AMD Zen 3 cpu (Retpoline),
> one Intel 10th Gen CPU (IBRS), one Intel 3rd Gen cpu (Retpoline) and one
> Intel Xeon CPU (IBRS) using pktgen with 64b udp packets. Our test setup is a
> dummy device with clsact and matchall in a kernel compiled with every
> tc module as built-in.  We observed a 3-8% speed up on the retpoline CPUs,
> when going through 1 tc filter, and a 60-100% speed up when going through 100 filters.
> For the IBRS cpus we observed a 1-2% degradation in both scenarios, we believe
> the extra branches check introduced a small overhead therefore we added
> a static key that bypasses the wrapper on kernels not using the retpoline mitigation,
> but compiled with CONFIG_RETPOLINE.

...

Re: [PATCH net-next v6 0/4] net/sched: retpoline wrappers for tc

[Pedro Tammela]

On 27/12/2022 05:33, Rudi Heitbaum wrote:
> Hi Pedro,
> 
> Compiling kernel 6.2-rc1 fails on x86_64 when CONFIG_NET_CLS or
> CONFIG_NET_CLS_ACT is not set, when CONFIG_RETPOLINE=y is set.
> 
> Does tc_wrapper RETPOLINE need a dependency on NET_CLS/NET_CLS_ACT
> to be added? Or a default?
> 
> net/sched/sch_api.c: In function 'pktsched_init':
> net/sched/sch_api.c:2306:9: error: implicit declaration of function
> 'tc_wrapper_init' [-Werror=implicit-function-declaration]
>   2306 |         tc_wrapper_init();
>        |         ^~~~~~~~~~~~~~~
> cc1: some warnings being treated as errors
> make[3]: *** [scripts/Makefile.build:252: net/sched/sch_api.o] Error 1
> make[2]: *** [scripts/Makefile.build:504: net/sched] Error 2
> make[1]: *** [scripts/Makefile.build:504: net] Error 2
> 
> below is the relevent lines from the .config file.
> 
> $ grep -e RETPOLINE -e NET_CLS projects/Generic/linux/linux.x86_64.conf
> CONFIG_RETPOLINE=y
> # CONFIG_NET_CLS_BASIC is not set
> # CONFIG_NET_CLS_TCINDEX is not set
> # CONFIG_NET_CLS_ROUTE4 is not set
> # CONFIG_NET_CLS_FW is not set
> # CONFIG_NET_CLS_U32 is not set
> # CONFIG_NET_CLS_RSVP is not set
> # CONFIG_NET_CLS_RSVP6 is not set
> # CONFIG_NET_CLS_FLOW is not set
> # CONFIG_NET_CLS_CGROUP is not set
> # CONFIG_NET_CLS_BPF is not set
> # CONFIG_NET_CLS_FLOWER is not set
> # CONFIG_NET_CLS_MATCHALL is not set
> # CONFIG_NET_CLS_ACT is not set
> 

Hi Rudi,

Thanks for the report.
Could you try the following patch?

diff --git a/include/net/tc_wrapper.h b/include/net/tc_wrapper.h
index ceed2fc089ff..d323fffb839a 100644
--- a/include/net/tc_wrapper.h
+++ b/include/net/tc_wrapper.h
@@ -216,6 +216,8 @@ static inline int tc_classify(struct sk_buff *skb, 
const struct tcf_proto *tp,
         return tp->classify(skb, tp, res);
  }

+#endif /* CONFIG_NET_CLS */
+
  static inline void tc_wrapper_init(void)
  {
  #ifdef CONFIG_X86
@@ -224,8 +226,6 @@ static inline void tc_wrapper_init(void)
  #endif
  }

-#endif /* CONFIG_NET_CLS */
-
  #else

  #define TC_INDIRECT_SCOPE static

Re: [PATCH net-next v6 0/4] net/sched: retpoline wrappers for tc

[Rudi Heitbaum]

On Tue, Dec 27, 2022 at 09:24:22AM -0300, Pedro Tammela wrote:
> On 27/12/2022 05:33, Rudi Heitbaum wrote:
> > Hi Pedro,
> > 
> > Compiling kernel 6.2-rc1 fails on x86_64 when CONFIG_NET_CLS or
> > CONFIG_NET_CLS_ACT is not set, when CONFIG_RETPOLINE=y is set.

...

> Hi Rudi,
> 
> Thanks for the report.
> Could you try the following patch?
> 
> diff --git a/include/net/tc_wrapper.h b/include/net/tc_wrapper.h
> index ceed2fc089ff..d323fffb839a 100644
> --- a/include/net/tc_wrapper.h
> +++ b/include/net/tc_wrapper.h
> @@ -216,6 +216,8 @@ static inline int tc_classify(struct sk_buff *skb, const
> struct tcf_proto *tp,
>         return tp->classify(skb, tp, res);
>  }
> 
> +#endif /* CONFIG_NET_CLS */
> +
>  static inline void tc_wrapper_init(void)
>  {
>  #ifdef CONFIG_X86
> @@ -224,8 +226,6 @@ static inline void tc_wrapper_init(void)
>  #endif
>  }
> 
> -#endif /* CONFIG_NET_CLS */
> -
>  #else
> 
>  #define TC_INDIRECT_SCOPE static

Hi Pedro,

I had to adjust it slightly to apply cleanly.
But works correctly with my .config now.

Thanks
Rudi

Tested-by: Rudi Heitbaum <rudi@heitbaum.com>

diff --git a/include/net/tc_wrapper.h b/include/net/tc_wrapper.h
index ceed2fc089ff..d323fffb839a 100644
--- a/include/net/tc_wrapper.h
+++ b/include/net/tc_wrapper.h
@@ -216,6 +216,8 @@
 	return tp->classify(skb, tp, res);
 }
 
+#endif /* CONFIG_NET_CLS */
+
 static inline void tc_wrapper_init(void)
 {
 #ifdef CONFIG_X86
@@ -224,8 +226,6 @@
 #endif
 }
 
-#endif /* CONFIG_NET_CLS */
-
 #else
 
 #define TC_INDIRECT_SCOPE static