From: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Vincent Mailhol <mailhol.vincent@wanadoo.fr>,
Jakub Kicinski <kuba@kernel.org>,
Oliver Neukum <oneukum@suse.com>,
Masahiro Yamada <masahiroy@kernel.org>,
Arunachalam Santhanam <arunachalam.santhanam@in.bosch.com>,
Marc Kleine-Budde <mkl@pengutronix.de>,
linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
linux-can@vger.kernel.org,
Wolfgang Grandegger <wg@grandegger.com>,
"David S . Miller" <davem@davemloft.net>
Subject: Re: [PATCH v2 5/6] can: usb: etas_es58X: add support for ETAS ES58X CAN USB interfaces
Date: Fri, 2 Oct 2020 00:56:41 +0900 [thread overview]
Message-ID: <20201001155641.3421-1-mailhol.vincent@wanadoo.fr> (raw)
In-Reply-To: <20200930161838.GB1663344@kroah.com>
> > + num_element =
> > + es58x_msg_num_element(es58x_dev->dev,
> > + bulk_rx_loopback_msg->rx_loopback_msg,
> > + msg_len);
> > + if (unlikely(num_element <= 0))
> > + return num_element;
>
> Meta-comment on your use of 'unlikely' everywhere. Please drop it, it's
> only to be used if you can actually measure the difference in a
> benchmark. You are dealing with USB devices, which are really really
> slow here. Also, humans make horrible guessers for this type of thing,
> the compiler and CPU can get this right much more often than we can, and
> we had the numbers for it (someone measured that 80-90% of our usages of
> these markings are actually wrong on modern cpus).
>
> So just drop them all, it makes the code simpler to read and understand,
> and the cpu can actually go faster.
All those branch on which the unlikely() macro were applied were
supposed to never been executed under normal circumstances. But I
indeed have no benchmark to claim such use.
Thank you for the detailed explanation, makes perfect sense. Each use
of the likely()/unlikely() macros will be removed in v3 revision.
next prev parent reply other threads:[~2020-10-01 15:57 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-26 17:57 [PATCH 0/6] can: add support for ETAS ES58X CAN USB Vincent Mailhol
2020-09-26 17:57 ` [PATCH 1/6] can: dev: can_get_echo_skb(): prevent call to kfree_skb() in hard IRQ context Vincent Mailhol
2020-09-26 17:57 ` [PATCH 2/6] can: dev: add a helper function to get the correct length of Classical frames Vincent Mailhol
2020-09-26 17:57 ` [PATCH 3/6] can: dev: __can_get_echo_skb(): fix the return length Vincent Mailhol
2020-09-26 17:57 ` [PATCH 4/6] can: dev: add a helper function to calculate the duration of one bit Vincent Mailhol
2020-09-26 17:57 ` [PATCH 5/6] can: usb: etas_es58X: add support for ETAS ES58X CAN USB interfaces Vincent Mailhol
2020-09-26 17:57 ` [PATCH 6/6] USB: cdc-acm: blacklist ETAS ES58X device Vincent Mailhol
2020-09-27 5:45 ` Greg Kroah-Hartman
2020-09-27 5:52 ` Greg Kroah-Hartman
2020-09-29 2:15 ` Vincent Mailhol
2020-09-30 14:45 ` [PATCH v2 0/6] can: add support for ETAS ES58X CAN USB Vincent Mailhol
2020-09-30 14:45 ` [PATCH v2 1/6] can: dev: can_get_echo_skb(): prevent call to kfree_skb() in hard IRQ context Vincent Mailhol
2020-09-30 14:45 ` [PATCH v2 2/6] can: dev: add a helper function to get the correct length of Classical frames Vincent Mailhol
2020-09-30 15:21 ` Marc Kleine-Budde
2020-10-01 15:45 ` [PATCH v2 2/6] can: dev: add a helper function Vincent Mailhol
2020-10-01 15:51 ` Marc Kleine-Budde
2020-09-30 14:45 ` [PATCH v2 3/6] can: dev: __can_get_echo_skb(): fix the return length Vincent Mailhol
2020-09-30 14:45 ` [PATCH v2 4/6] can: dev: add a helper function to calculate the duration of one bit Vincent Mailhol
2020-09-30 14:45 ` [PATCH v2 5/6] can: usb: etas_es58X: add support for ETAS ES58X CAN USB interfaces Vincent Mailhol
2020-09-30 16:18 ` Greg Kroah-Hartman
2020-10-01 15:56 ` Vincent Mailhol [this message]
2020-09-30 14:45 ` [PATCH v2 6/6] usb: cdc-acm: add quirk to blacklist ETAS ES58X devices Vincent Mailhol
2020-10-02 15:41 ` [PATCH v3 0/7] can: add support for ETAS ES58X CAN USB Vincent Mailhol
2020-10-02 15:41 ` [PATCH v3 1/7] can: dev: can_get_echo_skb(): prevent call to kfree_skb() in hard IRQ context Vincent Mailhol
2020-10-02 15:41 ` [PATCH v3 2/7] can: dev: fix type of get_can_dlc() and get_canfd_dlc() macros Vincent Mailhol
2020-10-02 15:41 ` [PATCH v3 3/7] can: dev: add a helper function to get the correct length of Classical frames Vincent Mailhol
2020-10-02 15:41 ` [PATCH v3 4/7] can: dev: __can_get_echo_skb(): fix the return length Vincent Mailhol
2020-10-02 15:41 ` [PATCH v3 5/7] can: dev: add a helper function to calculate the duration of one bit Vincent Mailhol
2020-10-04 11:06 ` Marc Kleine-Budde
2020-10-04 11:10 ` Marc Kleine-Budde
2020-10-02 15:41 ` [PATCH v3 6/7] can: usb: etas_es58X: add support for ETAS ES58X CAN USB interfaces Vincent Mailhol
2020-10-04 12:06 ` Marc Kleine-Budde
2020-10-10 8:12 ` Vincent Mailhol
2020-10-02 15:41 ` [PATCH v3 7/7] usb: cdc-acm: add quirk to blacklist ETAS ES58X devices Vincent Mailhol
2020-10-05 11:14 ` Greg Kroah-Hartman
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