From: Thomas Gleixner <tglx@linutronix.de>
To: Kurt Kanzenbach <kurt@linutronix.de>,
"David S. Miller" <davem@davemloft.net>,
Jakub Kicinski <kuba@kernel.org>
Cc: Giuseppe Cavallaro <peppe.cavallaro@st.com>,
Alexandre Torgue <alexandre.torgue@foss.st.com>,
Jose Abreu <joabreu@synopsys.com>,
Maxime Coquelin <mcoquelin.stm32@gmail.com>,
Voon Weifeng <weifeng.voon@intel.com>,
Ong Boon Leong <boon.leong.ong@intel.com>,
Wong Vee Khee <vee.khee.wong@linux.intel.com>,
Tan Tee Min <tee.min.tan@intel.com>,
"Wong, Vee Khee" <vee.khee.wong@intel.com>,
Xiaoliang Yang <xiaoliang.yang_1@nxp.com>,
netdev@vger.kernel.org, linux-stm32@st-md-mailman.stormreply.com,
linux-arm-kernel@lists.infradead.org,
Benedikt Spranger <b.spranger@linutronix.de>,
Kurt Kanzenbach <kurt@linutronix.de>
Subject: Re: [PATCH net-next v1] net: stmmac: Caclucate clock domain crossing error only once
Date: Fri, 19 Nov 2021 12:50:21 +0100 [thread overview]
Message-ID: <87mtm0l5z6.ffs@tglx> (raw)
In-Reply-To: <20211119081010.27084-1-kurt@linutronix.de>
Kurt,
On Fri, Nov 19 2021 at 09:10, Kurt Kanzenbach wrote:
> The clock domain crossing error (CDC) is calculated at every fetch of Tx or Rx
> timestamps. It includes a division. Especially on arm32 based systems it is
> expensive. It also saves the two conditionals.
This does not make sense. What you want to say here is:
It also requires two conditionals in the hotpath.
> Therefore, move the calculation to the PTP initialization code and just use the
> cached value in the timestamp retrieval functions.
Maybe:
Add a compensation value cache to struct plat_stmmacenet_data and
subtract it unconditionally in the RX/TX functions which spares the
conditionals.
The value is initialized to 0 and if supported calculated in the PTP
initialization code.
or something to that effect.
> + /* Calculate the clock domain crossing (CDC) error if necessary */
> + priv->plat->cdc_error_adj = 0;
> + if (priv->plat->has_gmac4 && priv->plat->clk_ptp_rate)
> + priv->plat->cdc_error_adj = (2 * NSEC_PER_SEC) /
> + priv->plat->clk_ptp_rate;
Nit. Just let stick it out. We lifted the 80 char limitation some time ago.
Thanks,
tglx
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WARNING: multiple messages have this Message-ID (diff)
From: Thomas Gleixner <tglx@linutronix.de>
To: Kurt Kanzenbach <kurt@linutronix.de>,
"David S. Miller" <davem@davemloft.net>,
Jakub Kicinski <kuba@kernel.org>
Cc: Giuseppe Cavallaro <peppe.cavallaro@st.com>,
Alexandre Torgue <alexandre.torgue@foss.st.com>,
Jose Abreu <joabreu@synopsys.com>,
Maxime Coquelin <mcoquelin.stm32@gmail.com>,
Voon Weifeng <weifeng.voon@intel.com>,
Ong Boon Leong <boon.leong.ong@intel.com>,
Wong Vee Khee <vee.khee.wong@linux.intel.com>,
Tan Tee Min <tee.min.tan@intel.com>,
"Wong, Vee Khee" <vee.khee.wong@intel.com>,
Xiaoliang Yang <xiaoliang.yang_1@nxp.com>,
netdev@vger.kernel.org, linux-stm32@st-md-mailman.stormreply.com,
linux-arm-kernel@lists.infradead.org,
Benedikt Spranger <b.spranger@linutronix.de>,
Kurt Kanzenbach <kurt@linutronix.de>
Subject: Re: [PATCH net-next v1] net: stmmac: Caclucate clock domain crossing error only once
Date: Fri, 19 Nov 2021 12:50:21 +0100 [thread overview]
Message-ID: <87mtm0l5z6.ffs@tglx> (raw)
In-Reply-To: <20211119081010.27084-1-kurt@linutronix.de>
Kurt,
On Fri, Nov 19 2021 at 09:10, Kurt Kanzenbach wrote:
> The clock domain crossing error (CDC) is calculated at every fetch of Tx or Rx
> timestamps. It includes a division. Especially on arm32 based systems it is
> expensive. It also saves the two conditionals.
This does not make sense. What you want to say here is:
It also requires two conditionals in the hotpath.
> Therefore, move the calculation to the PTP initialization code and just use the
> cached value in the timestamp retrieval functions.
Maybe:
Add a compensation value cache to struct plat_stmmacenet_data and
subtract it unconditionally in the RX/TX functions which spares the
conditionals.
The value is initialized to 0 and if supported calculated in the PTP
initialization code.
or something to that effect.
> + /* Calculate the clock domain crossing (CDC) error if necessary */
> + priv->plat->cdc_error_adj = 0;
> + if (priv->plat->has_gmac4 && priv->plat->clk_ptp_rate)
> + priv->plat->cdc_error_adj = (2 * NSEC_PER_SEC) /
> + priv->plat->clk_ptp_rate;
Nit. Just let stick it out. We lifted the 80 char limitation some time ago.
Thanks,
tglx
next prev parent reply other threads:[~2021-11-19 11:51 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-19 8:10 [PATCH net-next v1] net: stmmac: Caclucate clock domain crossing error only once Kurt Kanzenbach
2021-11-19 8:10 ` Kurt Kanzenbach
2021-11-19 11:50 ` Thomas Gleixner [this message]
2021-11-19 11:50 ` Thomas Gleixner
2021-11-19 12:00 ` Kurt Kanzenbach
2021-11-19 12:00 ` Kurt Kanzenbach
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