| Message ID | 2a6db6d6ca415cb35cc7b3e4d9424baf0516d782.1643902526.git.pabeni@redhat.com (mailing list archive) |
|---|---|
| State | Changes Requested |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | gro: some minor optimization | expand |
From: Paolo Abeni <pabeni@redhat.com> Date: Thu, 3 Feb 2022 16:48:22 +0100 > While inspecting some perf report, I noticed that the compiler > emits suboptimal code for the napi CB initialization, fetching > and storing multiple times the memory for flags bitfield. > This is with gcc 10.3.1, but I observed the same with older compiler > versions. > > We can help the compiler to do a nicer work clearing several > fields at once using an u32 alias. The generated code is quite > smaller, with the same number of conditional. > > Before: > objdump -t net/core/gro.o | grep " F .text" > 0000000000000bb0 l F .text 0000000000000357 dev_gro_receive > > After: > 0000000000000bb0 l F .text 000000000000033c dev_gro_receive > > RFC -> v1: > - use __struct_group to delimt the zeroed area (Alexander) "delimit"? > > Signed-off-by: Paolo Abeni <pabeni@redhat.com> > --- > include/net/gro.h | 52 +++++++++++++++++++++++++---------------------- > net/core/gro.c | 18 +++++++--------- > 2 files changed, 35 insertions(+), 35 deletions(-) > > diff --git a/include/net/gro.h b/include/net/gro.h > index 8f75802d50fd..fa1bb0f0ad28 100644 > --- a/include/net/gro.h > +++ b/include/net/gro.h > @@ -29,46 +29,50 @@ struct napi_gro_cb { > /* Number of segments aggregated. */ > u16 count; > > - /* Start offset for remote checksum offload */ > - u16 gro_remcsum_start; > + /* Used in ipv6_gro_receive() and foo-over-udp */ > + u16 proto; > > /* jiffies when first packet was created/queued */ > unsigned long age; > > - /* Used in ipv6_gro_receive() and foo-over-udp */ > - u16 proto; > + /* portion of the cb set to zero at every gro iteration */ > + __struct_group(/* no tag */, zeroed, /* no attrs */, Oh, only after sending this in my reply I noticed that there's a shorthand for this struct_group(name, ...) means exactly __struct_group(/* no tag */, name, /* no attrs */, ...) Sorry for that. I got confused by that Kees used __struct_group() directly in one place although there was a possibility to use short struct_group() instead. Since there should already be a v2 (see below), probably worth changing. > + > + /* Start offset for remote checksum offload */ > + u16 gro_remcsum_start; > > - /* This is non-zero if the packet may be of the same flow. */ > - u8 same_flow:1; > + /* This is non-zero if the packet may be of the same flow. */ > + u8 same_flow:1; > > - /* Used in tunnel GRO receive */ > - u8 encap_mark:1; > + /* Used in tunnel GRO receive */ > + u8 encap_mark:1; > > - /* GRO checksum is valid */ > - u8 csum_valid:1; > + /* GRO checksum is valid */ > + u8 csum_valid:1; > > - /* Number of checksums via CHECKSUM_UNNECESSARY */ > - u8 csum_cnt:3; > + /* Number of checksums via CHECKSUM_UNNECESSARY */ > + u8 csum_cnt:3; > > - /* Free the skb? */ > - u8 free:2; > + /* Free the skb? */ > + u8 free:2; > #define NAPI_GRO_FREE 1 > #define NAPI_GRO_FREE_STOLEN_HEAD 2 > > - /* Used in foo-over-udp, set in udp[46]_gro_receive */ > - u8 is_ipv6:1; > + /* Used in foo-over-udp, set in udp[46]_gro_receive */ > + u8 is_ipv6:1; > > - /* Used in GRE, set in fou/gue_gro_receive */ > - u8 is_fou:1; > + /* Used in GRE, set in fou/gue_gro_receive */ > + u8 is_fou:1; > > - /* Used to determine if flush_id can be ignored */ > - u8 is_atomic:1; > + /* Used to determine if flush_id can be ignored */ > + u8 is_atomic:1; > > - /* Number of gro_receive callbacks this packet already went through */ > - u8 recursion_counter:4; > + /* Number of gro_receive callbacks this packet already went through */ > + u8 recursion_counter:4; > > - /* GRO is done by frag_list pointer chaining. */ > - u8 is_flist:1; > + /* GRO is done by frag_list pointer chaining. */ > + u8 is_flist:1; > + ); > > /* used to support CHECKSUM_COMPLETE for tunneling protocols */ > __wsum csum; > diff --git a/net/core/gro.c b/net/core/gro.c > index d43d42215bdb..fc56be9408c7 100644 > --- a/net/core/gro.c > +++ b/net/core/gro.c > @@ -435,6 +435,9 @@ static void gro_flush_oldest(struct napi_struct *napi, struct list_head *head) > napi_gro_complete(napi, oldest); > } > > +#define zeroed_len (offsetof(struct napi_gro_cb, zeroed_end) - \ > + offsetof(struct napi_gro_cb, zeroed_start)) > + A leftover from the RFC I guess? It's not used anywhere in the code, so it doesn't break build. > static enum gro_result dev_gro_receive(struct napi_struct *napi, struct sk_buff *skb) > { > u32 bucket = skb_get_hash_raw(skb) & (GRO_HASH_BUCKETS - 1); > @@ -459,29 +462,22 @@ static enum gro_result dev_gro_receive(struct napi_struct *napi, struct sk_buff > > skb_set_network_header(skb, skb_gro_offset(skb)); > skb_reset_mac_len(skb); > - NAPI_GRO_CB(skb)->same_flow = 0; > + BUILD_BUG_ON(sizeof_field(struct napi_gro_cb, zeroed) != sizeof(u32)); > + BUILD_BUG_ON(!IS_ALIGNED(offsetof(struct napi_gro_cb, zeroed), > + sizeof(u32))); /* Avoid slow unaligned acc */ > + *(u32 *)&NAPI_GRO_CB(skb)->zeroed = 0; Looks relatively elegant and self-explanatory to me, nice. > NAPI_GRO_CB(skb)->flush = skb_is_gso(skb) || skb_has_frag_list(skb); > - NAPI_GRO_CB(skb)->free = 0; > - NAPI_GRO_CB(skb)->encap_mark = 0; > - NAPI_GRO_CB(skb)->recursion_counter = 0; > - NAPI_GRO_CB(skb)->is_fou = 0; > NAPI_GRO_CB(skb)->is_atomic = 1; > - NAPI_GRO_CB(skb)->gro_remcsum_start = 0; > > /* Setup for GRO checksum validation */ > switch (skb->ip_summed) { > case CHECKSUM_COMPLETE: > NAPI_GRO_CB(skb)->csum = skb->csum; > NAPI_GRO_CB(skb)->csum_valid = 1; > - NAPI_GRO_CB(skb)->csum_cnt = 0; > break; > case CHECKSUM_UNNECESSARY: > NAPI_GRO_CB(skb)->csum_cnt = skb->csum_level + 1; > - NAPI_GRO_CB(skb)->csum_valid = 0; > break; > - default: > - NAPI_GRO_CB(skb)->csum_cnt = 0; > - NAPI_GRO_CB(skb)->csum_valid = 0; > } > > pp = INDIRECT_CALL_INET(ptype->callbacks.gro_receive, > -- > 2.34.1 Al
On Thu, 2022-02-03 at 16:48 +0100, Paolo Abeni wrote: > While inspecting some perf report, I noticed that the compiler > emits suboptimal code for the napi CB initialization, fetching > and storing multiple times the memory for flags bitfield. > This is with gcc 10.3.1, but I observed the same with older compiler > versions. > > We can help the compiler to do a nicer work clearing several > fields at once using an u32 alias. The generated code is quite > smaller, with the same number of conditional. > > Before: > objdump -t net/core/gro.o | grep " F .text" > 0000000000000bb0 l F .text 0000000000000357 dev_gro_receive > > After: > 0000000000000bb0 l F .text 000000000000033c dev_gro_receive > > RFC -> v1: > - use __struct_group to delimt the zeroed area (Alexander) > > Signed-off-by: Paolo Abeni <pabeni@redhat.com> > --- > include/net/gro.h | 52 +++++++++++++++++++++++++-------------------- > -- > net/core/gro.c | 18 +++++++--------- > 2 files changed, 35 insertions(+), 35 deletions(-) > > diff --git a/include/net/gro.h b/include/net/gro.h > index 8f75802d50fd..fa1bb0f0ad28 100644 > --- a/include/net/gro.h > +++ b/include/net/gro.h > @@ -29,46 +29,50 @@ struct napi_gro_cb { > /* Number of segments aggregated. */ > u16 count; > > - /* Start offset for remote checksum offload */ > - u16 gro_remcsum_start; > + /* Used in ipv6_gro_receive() and foo-over-udp */ > + u16 proto; > > /* jiffies when first packet was created/queued */ > unsigned long age; > > - /* Used in ipv6_gro_receive() and foo-over-udp */ > - u16 proto; > + /* portion of the cb set to zero at every gro iteration */ > + __struct_group(/* no tag */, zeroed, /* no attrs */, Any specific reason for using __struct_group here rather than the struct_group macro instead?
On Thu, 2022-02-03 at 08:39 -0800, Alexander H Duyck wrote: > On Thu, 2022-02-03 at 16:48 +0100, Paolo Abeni wrote: > > While inspecting some perf report, I noticed that the compiler > > emits suboptimal code for the napi CB initialization, fetching > > and storing multiple times the memory for flags bitfield. > > This is with gcc 10.3.1, but I observed the same with older compiler > > versions. > > > > We can help the compiler to do a nicer work clearing several > > fields at once using an u32 alias. The generated code is quite > > smaller, with the same number of conditional. > > > > Before: > > objdump -t net/core/gro.o | grep " F .text" > > 0000000000000bb0 l F .text 0000000000000357 dev_gro_receive > > > > After: > > 0000000000000bb0 l F .text 000000000000033c dev_gro_receive > > > > RFC -> v1: > > - use __struct_group to delimt the zeroed area (Alexander) > > > > Signed-off-by: Paolo Abeni <pabeni@redhat.com> > > --- > > include/net/gro.h | 52 +++++++++++++++++++++++++-------------------- > > -- > > net/core/gro.c | 18 +++++++--------- > > 2 files changed, 35 insertions(+), 35 deletions(-) > > > > diff --git a/include/net/gro.h b/include/net/gro.h > > index 8f75802d50fd..fa1bb0f0ad28 100644 > > --- a/include/net/gro.h > > +++ b/include/net/gro.h > > @@ -29,46 +29,50 @@ struct napi_gro_cb { > > /* Number of segments aggregated. */ > > u16 count; > > > > - /* Start offset for remote checksum offload */ > > - u16 gro_remcsum_start; > > + /* Used in ipv6_gro_receive() and foo-over-udp */ > > + u16 proto; > > > > /* jiffies when first packet was created/queued */ > > unsigned long age; > > > > - /* Used in ipv6_gro_receive() and foo-over-udp */ > > - u16 proto; > > + /* portion of the cb set to zero at every gro iteration */ > > + __struct_group(/* no tag */, zeroed, /* no attrs */, > > Any specific reason for using __struct_group here rather than the > struct_group macro instead? Just sheer ignorance on my side. I'll fix on the next iteration. Thanks! Paolo
diff --git a/include/net/gro.h b/include/net/gro.h index 8f75802d50fd..fa1bb0f0ad28 100644 --- a/include/net/gro.h +++ b/include/net/gro.h @@ -29,46 +29,50 @@ struct napi_gro_cb { /* Number of segments aggregated. */ u16 count; - /* Start offset for remote checksum offload */ - u16 gro_remcsum_start; + /* Used in ipv6_gro_receive() and foo-over-udp */ + u16 proto; /* jiffies when first packet was created/queued */ unsigned long age; - /* Used in ipv6_gro_receive() and foo-over-udp */ - u16 proto; + /* portion of the cb set to zero at every gro iteration */ + __struct_group(/* no tag */, zeroed, /* no attrs */, + + /* Start offset for remote checksum offload */ + u16 gro_remcsum_start; - /* This is non-zero if the packet may be of the same flow. */ - u8 same_flow:1; + /* This is non-zero if the packet may be of the same flow. */ + u8 same_flow:1; - /* Used in tunnel GRO receive */ - u8 encap_mark:1; + /* Used in tunnel GRO receive */ + u8 encap_mark:1; - /* GRO checksum is valid */ - u8 csum_valid:1; + /* GRO checksum is valid */ + u8 csum_valid:1; - /* Number of checksums via CHECKSUM_UNNECESSARY */ - u8 csum_cnt:3; + /* Number of checksums via CHECKSUM_UNNECESSARY */ + u8 csum_cnt:3; - /* Free the skb? */ - u8 free:2; + /* Free the skb? */ + u8 free:2; #define NAPI_GRO_FREE 1 #define NAPI_GRO_FREE_STOLEN_HEAD 2 - /* Used in foo-over-udp, set in udp[46]_gro_receive */ - u8 is_ipv6:1; + /* Used in foo-over-udp, set in udp[46]_gro_receive */ + u8 is_ipv6:1; - /* Used in GRE, set in fou/gue_gro_receive */ - u8 is_fou:1; + /* Used in GRE, set in fou/gue_gro_receive */ + u8 is_fou:1; - /* Used to determine if flush_id can be ignored */ - u8 is_atomic:1; + /* Used to determine if flush_id can be ignored */ + u8 is_atomic:1; - /* Number of gro_receive callbacks this packet already went through */ - u8 recursion_counter:4; + /* Number of gro_receive callbacks this packet already went through */ + u8 recursion_counter:4; - /* GRO is done by frag_list pointer chaining. */ - u8 is_flist:1; + /* GRO is done by frag_list pointer chaining. */ + u8 is_flist:1; + ); /* used to support CHECKSUM_COMPLETE for tunneling protocols */ __wsum csum; diff --git a/net/core/gro.c b/net/core/gro.c index d43d42215bdb..fc56be9408c7 100644 --- a/net/core/gro.c +++ b/net/core/gro.c @@ -435,6 +435,9 @@ static void gro_flush_oldest(struct napi_struct *napi, struct list_head *head) napi_gro_complete(napi, oldest); } +#define zeroed_len (offsetof(struct napi_gro_cb, zeroed_end) - \ + offsetof(struct napi_gro_cb, zeroed_start)) + static enum gro_result dev_gro_receive(struct napi_struct *napi, struct sk_buff *skb) { u32 bucket = skb_get_hash_raw(skb) & (GRO_HASH_BUCKETS - 1); @@ -459,29 +462,22 @@ static enum gro_result dev_gro_receive(struct napi_struct *napi, struct sk_buff skb_set_network_header(skb, skb_gro_offset(skb)); skb_reset_mac_len(skb); - NAPI_GRO_CB(skb)->same_flow = 0; + BUILD_BUG_ON(sizeof_field(struct napi_gro_cb, zeroed) != sizeof(u32)); + BUILD_BUG_ON(!IS_ALIGNED(offsetof(struct napi_gro_cb, zeroed), + sizeof(u32))); /* Avoid slow unaligned acc */ + *(u32 *)&NAPI_GRO_CB(skb)->zeroed = 0; NAPI_GRO_CB(skb)->flush = skb_is_gso(skb) || skb_has_frag_list(skb); - NAPI_GRO_CB(skb)->free = 0; - NAPI_GRO_CB(skb)->encap_mark = 0; - NAPI_GRO_CB(skb)->recursion_counter = 0; - NAPI_GRO_CB(skb)->is_fou = 0; NAPI_GRO_CB(skb)->is_atomic = 1; - NAPI_GRO_CB(skb)->gro_remcsum_start = 0; /* Setup for GRO checksum validation */ switch (skb->ip_summed) { case CHECKSUM_COMPLETE: NAPI_GRO_CB(skb)->csum = skb->csum; NAPI_GRO_CB(skb)->csum_valid = 1; - NAPI_GRO_CB(skb)->csum_cnt = 0; break; case CHECKSUM_UNNECESSARY: NAPI_GRO_CB(skb)->csum_cnt = skb->csum_level + 1; - NAPI_GRO_CB(skb)->csum_valid = 0; break; - default: - NAPI_GRO_CB(skb)->csum_cnt = 0; - NAPI_GRO_CB(skb)->csum_valid = 0; } pp = INDIRECT_CALL_INET(ptype->callbacks.gro_receive,
While inspecting some perf report, I noticed that the compiler emits suboptimal code for the napi CB initialization, fetching and storing multiple times the memory for flags bitfield. This is with gcc 10.3.1, but I observed the same with older compiler versions. We can help the compiler to do a nicer work clearing several fields at once using an u32 alias. The generated code is quite smaller, with the same number of conditional. Before: objdump -t net/core/gro.o | grep " F .text" 0000000000000bb0 l F .text 0000000000000357 dev_gro_receive After: 0000000000000bb0 l F .text 000000000000033c dev_gro_receive RFC -> v1: - use __struct_group to delimt the zeroed area (Alexander) Signed-off-by: Paolo Abeni <pabeni@redhat.com> --- include/net/gro.h | 52 +++++++++++++++++++++++++---------------------- net/core/gro.c | 18 +++++++--------- 2 files changed, 35 insertions(+), 35 deletions(-)