On 30/05/2023 14.17, Tariq Toukan wrote:
On 30/05/2023 14:33, Jesper Dangaard Brouer wrote:
On 29/05/2023 13.06, Tariq Toukan wrote:
Expand the xdp multi-buffer support to xdp_redirect tool.
Similar to what's done in commit
772251742262 ("samples/bpf: fixup some tools to be able to support
xdp multibuffer")
and its fix commit
7a698edf954c ("samples/bpf: Fix MAC address swapping in xdp2_kern").
Have you tested if this cause a performance degradation?
(Also found possible bug below)
Hi Jesper,
This introduces the same known perf degradation we already have in xdp1
and xdp2.
Did a quick test with xdp1, the performance degradation is around 18%.
Before: 22,917,961 pps
After: 18,798,336 pps
(1-(18798336/22917961))*100 = 17.97%
Unfortunately, this is the API we have today to safely support
multi-buffer.
Note that both perf and functional (noted below) degradation should be
eliminated once replacing the load/store operations with dynptr logic
that returns a pointer to the scatter entry instead of copying it.
Well, should we use dynptr logic in this patch then?
Does it make sense to add sample code that does thing in a way that is
sub-optimal and we want to replace?
... (I fear people will copy paste the sample code).
I initiated a discussion on this topic a few months ago. dynptr was
accepted since then, but I'm not aware of any in-progress followup work
that addresses this.
Are you saying some more work is needed on dynptr?
Signed-off-by: Tariq Toukan <tariqt@xxxxxxxxxx>
Reviewed-by: Nimrod Oren <noren@xxxxxxxxxx>
---
samples/bpf/xdp_redirect.bpf.c | 16 ++++++++++++----
1 file changed, 12 insertions(+), 4 deletions(-)
diff --git a/samples/bpf/xdp_redirect.bpf.c
b/samples/bpf/xdp_redirect.bpf.c
index 7c02bacfe96b..620163eb7e19 100644
--- a/samples/bpf/xdp_redirect.bpf.c
+++ b/samples/bpf/xdp_redirect.bpf.c
@@ -16,16 +16,21 @@
const volatile int ifindex_out;
-SEC("xdp")
+#define XDPBUFSIZE 64
Pktgen sample scripts will default send with 60 pkt length, because the
4 bytes FCS (end-frame checksum) is added by hardware.
Will this result in an error when bpf_xdp_load_bytes() tries to copy 64
bytes from a 60 bytes packet?
Yes.
This can be resolved by reducing XDPBUFSIZE to 60.
Need to check if it's OK to disregard these last 4 bytes without hurting
the XDP program logic.
If so, do you suggest changing xdp1 and xdp2 as well?
I can take care of reducing XDPBUFSIZE to 60 on xpd1 and xdp2, as I
already had to make these changes for the above quick bench work ;-)
I'll send out patches shortly.
+SEC("xdp.frags")
int xdp_redirect_prog(struct xdp_md *ctx)
{
- void *data_end = (void *)(long)ctx->data_end;
- void *data = (void *)(long)ctx->data;
+ __u8 pkt[XDPBUFSIZE] = {};
+ void *data_end = &pkt[XDPBUFSIZE-1];
+ void *data = pkt;
u32 key = bpf_get_smp_processor_id();
struct ethhdr *eth = data;
struct datarec *rec;
u64 nh_off;
+ if (bpf_xdp_load_bytes(ctx, 0, pkt, sizeof(pkt)))
+ return XDP_DROP;
E.g. sizeof(pkt) = 64 bytes here.
+
nh_off = sizeof(*eth);
if (data + nh_off > data_end)
return XDP_DROP;
@@ -36,11 +41,14 @@ int xdp_redirect_prog(struct xdp_md *ctx)
NO_TEAR_INC(rec->processed);
swap_src_dst_mac(data);
+ if (bpf_xdp_store_bytes(ctx, 0, pkt, sizeof(pkt)))
+ return XDP_DROP;
+
return bpf_redirect(ifindex_out, 0);
}
/* Redirect require an XDP bpf_prog loaded on the TX device */
-SEC("xdp")
+SEC("xdp.frags")
int xdp_redirect_dummy_prog(struct xdp_md *ctx)
{
return XDP_PASS;
