From: "Morten Brørup" <mb@smartsharesystems.com>
To: "Stephen Hemminger" <stephen@networkplumber.org>,
"Ferruh Yigit" <ferruh.yigit@amd.com>
Cc: "Sivaprasad Tummala" <sivaprasad.tummala@amd.com>,
<david.marchand@redhat.com>, <aman.deep.singh@intel.com>,
<yuying.zhang@intel.com>, <dev@dpdk.org>, <stable@dpdk.org>
Subject: RE: [PATCH v2] app/testpmd: fix lcore ID restriction
Date: Fri, 14 Jun 2024 19:50:29 +0200 [thread overview]
Message-ID: <98CBD80474FA8B44BF855DF32C47DC35E9F523@smartserver.smartshare.dk> (raw)
In-Reply-To: <20240614082707.3a2becec@hermes.local>
> From: Stephen Hemminger [mailto:stephen@networkplumber.org]
> Sent: Friday, 14 June 2024 17.27
>
> On Fri, 14 Jun 2024 10:01:02 +0100
> Ferruh Yigit <ferruh.yigit@amd.com> wrote:
>
> > On 6/13/2024 8:13 PM, Stephen Hemminger wrote:
> > > On Thu, 13 Jun 2024 17:51:14 +0100
> > > Ferruh Yigit <ferruh.yigit@amd.com> wrote:
> > >
> > >>> Hi Sivaprasad,
> > >>>
> > >>> Is this '(lcoreid_t)' cast required? Because of integer promotion
> I
> > >>> think result will be correct without casting.
> > >>>
> > >>> (And without integer promotion considered, casting needs to be
> done on
> > >>> one of the variables, not to the result, because result may be
> already
> > >>> cast down I think. Anyway this is not required for this case since
> > >>> variables are u16.)
> > >>>
> > >>
> > >> Why casing required (for record) is,
> > >> 'nb_txq' -> uint16_t, promoted to 'int'
> > >> 'nb_fwd_ports' -> uint16_t, promoted to 'int'
> > >> (nb_txq * nb_fwd_ports) -> result 'int'
> > >> nb_fwd_lcores -> 'uint32_t'
> > >>
> > >> comparison between 'int' & 'uint32_t' gives warning. After some
> compiler
> > >> version it is smart enough to not give a warning, but casting is
> > >> required for old compilers.
> > >>
> > >> And back to my comment above, casting one of the parameter to
> > >> 'lcoreid_t' also works, as it forcing promotion to 'unsigned int'
> > >> instead. But logically casting looks odd, so keeping casting
> result.
> > >
> > > Where is the integer promotion happening?
> > >
> >
> > Raslan reported following compile error, this version of the patch has
> > the cast, but merged version, v3, doesn't.
> >
> >
> > ```
> > ../../root/dpdk/app/test-pmd/config.c: In function
> 'icmp_echo_config_setup':
> > ../../root/dpdk/app/test-pmd/config.c:5159:30: error: comparison
> between
> > signed and unsigned integer expressions [-Werror=sign-compare]
> > if ((nb_txq * nb_fwd_ports) < nb_fwd_lcores)
>
> That does look like a compiler bug. uint16 multiplied by uint16 should
> be uint16.
Not, C doesn't promote types like that. Arithmetic operations always promote smaller types to int or unsigned int. And since uint16 fits in int, uint16 is promoted to int (not unsigned int).
> Not sure why DPDK keeps using small types like uint16 so much, doesn't
> have any
> real benefit since all this is in registers.
next prev parent reply other threads:[~2024-06-14 17:50 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-15 19:46 [PATCH] " Sivaprasad Tummala
2024-04-15 21:54 ` Stephen Hemminger
2024-04-15 21:56 ` Stephen Hemminger
2024-04-16 9:55 ` [PATCH v2] " Sivaprasad Tummala
2024-04-19 8:24 ` Ferruh Yigit
2024-04-19 11:30 ` Ferruh Yigit
2024-06-06 9:56 ` Tummala, Sivaprasad
2024-06-13 16:51 ` Ferruh Yigit
2024-06-13 19:13 ` Stephen Hemminger
2024-06-14 9:01 ` Ferruh Yigit
2024-06-14 15:27 ` Stephen Hemminger
2024-06-14 15:39 ` Ferruh Yigit
2024-06-14 17:50 ` Morten Brørup [this message]
2024-06-14 18:11 ` Stephen Hemminger
2024-06-06 11:27 ` [PATCH v3] " Sivaprasad Tummala
2024-06-11 23:37 ` Ferruh Yigit
2024-06-13 16:36 ` Ferruh Yigit
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