* [PATCH] bpf: devmap: hoist loop-invariant xdp buff pointer setup
@ 2026-02-16 14:53 Anand Kumar Shaw
2026-02-20 2:53 ` Alexei Starovoitov
0 siblings, 1 reply; 2+ messages in thread
From: Anand Kumar Shaw @ 2026-02-16 14:53 UTC (permalink / raw)
To: bpf
Cc: netdev, ast, daniel, hawk, john.fastabend, kuba, davem, sdf,
andrii, martin.lau, Anand Kumar Shaw
In dev_map_bpf_prog_run(), xdp.txq and xdp.rxq are assigned the same
stack-local pointers on every iteration. xdp_convert_frame_to_buff()
does not modify these fields, so the assignments are loop-invariant.
Hoist them before the loop, matching the pattern already used by
cpu_map_bpf_prog_run_xdp() in cpumap.c.
No functional change.
Signed-off-by: Anand Kumar Shaw <anandkrshawheritage@gmail.com>
---
kernel/bpf/devmap.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
index 2625601de..568477ce7 100644
--- a/kernel/bpf/devmap.c
+++ b/kernel/bpf/devmap.c
@@ -341,14 +341,15 @@ static int dev_map_bpf_prog_run(struct bpf_prog *xdp_prog,
struct xdp_buff xdp;
int i, nframes = 0;
+ xdp.txq = &txq;
+ xdp.rxq = &rxq;
+
for (i = 0; i < n; i++) {
struct xdp_frame *xdpf = frames[i];
u32 act;
int err;
xdp_convert_frame_to_buff(xdpf, &xdp);
- xdp.txq = &txq;
- xdp.rxq = &rxq;
act = bpf_prog_run_xdp(xdp_prog, &xdp);
switch (act) {
--
2.39.5 (Apple Git-154)
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] bpf: devmap: hoist loop-invariant xdp buff pointer setup
2026-02-16 14:53 [PATCH] bpf: devmap: hoist loop-invariant xdp buff pointer setup Anand Kumar Shaw
@ 2026-02-20 2:53 ` Alexei Starovoitov
0 siblings, 0 replies; 2+ messages in thread
From: Alexei Starovoitov @ 2026-02-20 2:53 UTC (permalink / raw)
To: Anand Kumar Shaw
Cc: bpf, Network Development, Alexei Starovoitov, Daniel Borkmann,
Jesper Dangaard Brouer, John Fastabend, Jakub Kicinski,
David S. Miller, Stanislav Fomichev, Andrii Nakryiko,
Martin KaFai Lau
On Mon, Feb 16, 2026 at 6:53 AM Anand Kumar Shaw
<anandkrshawheritage@gmail.com> wrote:
>
> In dev_map_bpf_prog_run(), xdp.txq and xdp.rxq are assigned the same
> stack-local pointers on every iteration. xdp_convert_frame_to_buff()
> does not modify these fields, so the assignments are loop-invariant.
>
> Hoist them before the loop, matching the pattern already used by
> cpu_map_bpf_prog_run_xdp() in cpumap.c.
>
> No functional change.
>
> Signed-off-by: Anand Kumar Shaw <anandkrshawheritage@gmail.com>
> ---
> kernel/bpf/devmap.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
> index 2625601de..568477ce7 100644
> --- a/kernel/bpf/devmap.c
> +++ b/kernel/bpf/devmap.c
> @@ -341,14 +341,15 @@ static int dev_map_bpf_prog_run(struct bpf_prog *xdp_prog,
> struct xdp_buff xdp;
> int i, nframes = 0;
>
> + xdp.txq = &txq;
> + xdp.rxq = &rxq;
> +
> for (i = 0; i < n; i++) {
> struct xdp_frame *xdpf = frames[i];
> u32 act;
> int err;
>
> xdp_convert_frame_to_buff(xdpf, &xdp);
> - xdp.txq = &txq;
> - xdp.rxq = &rxq;
Compilers are smart enough to hoist on their own,
but with this change the humans would have to think harder whether
xdp_convert_frame_to_buff() doesn't touch these two fields.
pw-bot: cr
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