linux-kernel - Re: [PATCH net-next 02/15] net: dsa: sja1105: Remove usage of iterator for list

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Date:   Sun, 10 Apr 2022 23:34:57 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Jakob Koschel <jakobkoschel@...il.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Lars Povlsen <lars.povlsen@...rochip.com>,
        Steen Hegelund <Steen.Hegelund@...rochip.com>,
        UNGLinuxDriver@...rochip.com, Ariel Elior <aelior@...vell.com>,
        Manish Chopra <manishc@...vell.com>,
        Edward Cree <ecree.xilinx@...il.com>,
        Martin Habets <habetsm.xilinx@...il.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Jiri Pirko <jiri@...nulli.us>,
        Casper Andersson <casper.casan@...il.com>,
        Bjarni Jonasson <bjarni.jonasson@...rochip.com>,
        Colin Ian King <colin.king@...el.com>,
        Michael Walle <michael@...le.cc>,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        Arnd Bergmann <arnd@...db.de>,
        Eric Dumazet <edumazet@...gle.com>,
        Xu Wang <vulab@...as.ac.cn>, Netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Mike Rapoport <rppt@...nel.org>,
        Brian Johannesmeyer <bjohannesmeyer@...il.com>,
        Cristiano Giuffrida <c.giuffrida@...nl>,
        "Bos, H.J." <h.j.bos@...nl>
Subject: Re: [PATCH net-next 02/15] net: dsa: sja1105: Remove usage of
 iterator for list_add() after loop

On Sun, Apr 10, 2022 at 10:30:31PM +0200, Jakob Koschel wrote:
> > On 10. Apr 2022, at 22:02, Vladimir Oltean <olteanv@...il.com> wrote:
> > 
> > On Sun, Apr 10, 2022 at 08:24:37PM +0200, Jakob Koschel wrote:
> >> Btw, I just realized that the if (!pos) is not necessary. This should simply do it:
> >> 
> >> diff --git a/drivers/net/dsa/sja1105/sja1105_vl.c b/drivers/net/dsa/sja1105/sja1105_vl.c
> >> index b7e95d60a6e4..2d59e75a9e3d 100644
> >> --- a/drivers/net/dsa/sja1105/sja1105_vl.c
> >> +++ b/drivers/net/dsa/sja1105/sja1105_vl.c
> >> @@ -28,6 +28,7 @@ static int sja1105_insert_gate_entry(struct sja1105_gating_config *gating_cfg,
> >> 		list_add(&e->list, &gating_cfg->entries);
> >> 	} else {
> >> +		struct list_head *pos = &gating_cfg->entries;
> >> 		struct sja1105_gate_entry *p;
> >> 
> >> 		list_for_each_entry(p, &gating_cfg->entries, list) {
> >> 			if (p->interval == e->interval) {
> >> @@ -37,10 +38,12 @@ static int sja1105_insert_gate_entry(struct sja1105_gating_config *gating_cfg,
> >> 				goto err;
> >> 			}
> >> 
> >> -			if (e->interval < p->interval)
> >> +			if (e->interval < p->interval) {
> >> +				pos = &p->list;
> >> 				break;
> >> +			}
> >> 		}
> >> -		list_add(&e->list, p->list.prev);
> >> +		list_add(&e->list, pos->prev);
> >> 	}
> >> 
> >> 	gating_cfg->num_entries++;
> >> -- 
> >> 2.25.1
> > 
> > I think we can give this a turn that is actually beneficial for the driver.
> > I've prepared and tested 3 patches on this function, see below.
> > Concrete improvements:
> > - that thing with list_for_each_entry() and list_for_each()
> > - no more special-casing of an empty list
> > - simplifying the error path
> > - that thing with list_add_tail()
> > 
> > What do you think about the changes below?
> 
> Thanks for all the good cooperation and help. The changes look great.
> I'll include them in v2 unless you want to do that separately, then I'll
> just remove them from the patch series.

I think it's less of a synchronization hassle if you send them along
with your list of others. Good luck.