netdev - Re: [PATCH v2 bpf-next] selftests: xsk: read current MAX_SKB

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Message-ID: <CAJ8uoz3tx60yLdwujSa2kmAvB+i7tj+HL-BAHgdcRMrXuq_fVA@mail.gmail.com>
Date: Tue, 10 Sep 2024 15:30:51 +0200
From: Magnus Karlsson <magnus.karlsson@...il.com>
To: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
Cc: bpf@...r.kernel.org, ast@...nel.org, daniel@...earbox.net, 
	andrii@...nel.org, netdev@...r.kernel.org, magnus.karlsson@...el.com, 
	bjorn@...nel.org
Subject: Re: [PATCH v2 bpf-next] selftests: xsk: read current MAX_SKB_FRAGS
 from sysctl knob

On Tue, 10 Sept 2024 at 14:41, Maciej Fijalkowski
<maciej.fijalkowski@...el.com> wrote:
>
> Currently, xskxceiver assumes that MAX_SKB_FRAGS value is always 17
> which is not true - since the introduction of BIG TCP this can now take
> any value between 17 to 45 via CONFIG_MAX_SKB_FRAGS.
>
> Adjust the TOO_MANY_FRAGS test case to read the currently configured
> MAX_SKB_FRAGS value by reading it from /proc/sys/net/core/max_skb_frags.
> If running system does not provide that sysctl file then let us try
> running the test with a default value.

Acked-by: Magnus Karlsson <magnus.karlsson@...el.com>

> Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
> ---
>
> v2: instead of failing the test case when reading frag value from sysctl
>     file did not succeed, use a default count and proceed with test [Magnus]
>
>  tools/testing/selftests/bpf/xskxceiver.c | 43 +++++++++++++++++++++---
>  tools/testing/selftests/bpf/xskxceiver.h |  1 -
>  2 files changed, 38 insertions(+), 6 deletions(-)
>
> diff --git a/tools/testing/selftests/bpf/xskxceiver.c b/tools/testing/selftests/bpf/xskxceiver.c
> index 92af633faea8..11f047b8af75 100644
> --- a/tools/testing/selftests/bpf/xskxceiver.c
> +++ b/tools/testing/selftests/bpf/xskxceiver.c
> @@ -325,6 +325,25 @@ static bool ifobj_zc_avail(struct ifobject *ifobject)
>         return zc_avail;
>  }
>
> +#define MAX_SKB_FRAGS_PATH "/proc/sys/net/core/max_skb_frags"
> +static unsigned int get_max_skb_frags(void)
> +{
> +       unsigned int max_skb_frags = 0;
> +       FILE *file;
> +
> +       file = fopen(MAX_SKB_FRAGS_PATH, "r");
> +       if (!file) {
> +               ksft_print_msg("Error opening %s\n", MAX_SKB_FRAGS_PATH);
> +               return 0;
> +       }
> +
> +       if (fscanf(file, "%u", &max_skb_frags) != 1)
> +               ksft_print_msg("Error reading %s\n", MAX_SKB_FRAGS_PATH);
> +
> +       fclose(file);
> +       return max_skb_frags;
> +}
> +
>  static struct option long_options[] = {
>         {"interface", required_argument, 0, 'i'},
>         {"busy-poll", no_argument, 0, 'b'},
> @@ -2245,13 +2264,24 @@ static int testapp_poll_rxq_tmout(struct test_spec *test)
>
>  static int testapp_too_many_frags(struct test_spec *test)
>  {
> -       struct pkt pkts[2 * XSK_DESC__MAX_SKB_FRAGS + 2] = {};
> +       struct pkt *pkts;
>         u32 max_frags, i;
> +       int ret;
>
> -       if (test->mode == TEST_MODE_ZC)
> +       if (test->mode == TEST_MODE_ZC) {
>                 max_frags = test->ifobj_tx->xdp_zc_max_segs;
> -       else
> -               max_frags = XSK_DESC__MAX_SKB_FRAGS;
> +       } else {
> +               max_frags = get_max_skb_frags();
> +               if (!max_frags) {
> +                       ksft_print_msg("Couldn't retrieve MAX_SKB_FRAGS from system, using default (17) value\n");
> +                       max_frags = 17;
> +               }
> +               max_frags += 1;
> +       }
> +
> +       pkts = calloc(2 * max_frags + 2, sizeof(struct pkt));
> +       if (!pkts)
> +               return TEST_FAILURE;
>
>         test->mtu = MAX_ETH_JUMBO_SIZE;
>
> @@ -2281,7 +2311,10 @@ static int testapp_too_many_frags(struct test_spec *test)
>         pkts[2 * max_frags + 1].valid = true;
>
>         pkt_stream_generate_custom(test, pkts, 2 * max_frags + 2);
> -       return testapp_validate_traffic(test);
> +       ret = testapp_validate_traffic(test);
> +
> +       free(pkts);
> +       return ret;
>  }
>
>  static int xsk_load_xdp_programs(struct ifobject *ifobj)
> diff --git a/tools/testing/selftests/bpf/xskxceiver.h b/tools/testing/selftests/bpf/xskxceiver.h
> index 885c948c5d83..e46e823f6a1a 100644
> --- a/tools/testing/selftests/bpf/xskxceiver.h
> +++ b/tools/testing/selftests/bpf/xskxceiver.h
> @@ -55,7 +55,6 @@
>  #define XSK_UMEM__LARGE_FRAME_SIZE (3 * 1024)
>  #define XSK_UMEM__MAX_FRAME_SIZE (4 * 1024)
>  #define XSK_DESC__INVALID_OPTION (0xffff)
> -#define XSK_DESC__MAX_SKB_FRAGS 18
>  #define HUGEPAGE_SIZE (2 * 1024 * 1024)
>  #define PKT_DUMP_NB_TO_PRINT 16
>  #define RUN_ALL_TESTS UINT_MAX
> --
> 2.34.1
>
>