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Subject: RE: [PATCH v2] eal: avoid issues in macro expansion of alignment
Date: Tue, 4 Jul 2023 10:43:40 +0200
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Thread-Topic: [PATCH v2] eal: avoid issues in macro expansion of alignment
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From: =?iso-8859-1?Q?Morten_Br=F8rup?= <mb@smartsharesystems.com>
To: "Stephen Hemminger" <stephen@networkplumber.org>,
	<dev@dpdk.org>
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> From: Stephen Hemminger [mailto:stephen@networkplumber.org]
> Sent: Tuesday, 4 July 2023 01.24
>=20
> RTE_ALIGN_MUL_NEAR is a macro so the cycle argument could
> get evaluated twice causing some potential skew.  Fix by
> computing value once.
>=20
> Suggested by patch to fix side effects.
>=20
> Fixes: 5cbd14b3e5f9 ("eal: roundup TSC frequency when estimating")
> Cc: pbhagavatula@marvell.com
> Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
> ---
> v2 - fix spelling error in commit message
>=20
>  lib/eal/common/eal_common_timer.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
>=20
> diff --git a/lib/eal/common/eal_common_timer.c
> b/lib/eal/common/eal_common_timer.c
> index 5686a5102b66..05614b0503cf 100644
> --- a/lib/eal/common/eal_common_timer.c
> +++ b/lib/eal/common/eal_common_timer.c
> @@ -42,10 +42,14 @@ estimate_tsc_freq(void)
>  	RTE_LOG(WARNING, EAL, "WARNING: TSC frequency estimated roughly"
>  		" - clock timings may be less accurate.\n");
>  	/* assume that the rte_delay_us_sleep() will sleep for 1 second */
> -	uint64_t start =3D rte_rdtsc();
> +	uint64_t start, elapsed;
> +
> +	start =3D rte_rdtsc();
>  	rte_delay_us_sleep(US_PER_S);
> +	elapsed =3D rte_rdtsc() - start;
> +
>  	/* Round up to 10Mhz. 1E7 ~ 10Mhz */
> -	return RTE_ALIGN_MUL_NEAR(rte_rdtsc() - start, CYC_PER_10MHZ);
> +	return RTE_ALIGN_MUL_NEAR(elapsed, CYC_PER_10MHZ);
>  }
>=20
>  void
> --
> 2.39.2

Please fix the RTE_ALIGN_MUL_NEAR() macro instead. It already uses =
temporary variables with typeof() anyway.

Other macros might have similar behavior of using their parameters more =
than once, and could be improved too.