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Date: Fri, 28 Aug 2015 12:20:54 -0700 From: Joe Perches <joe@...ches.com> To: David Miller <davem@...emloft.net> Cc: raghavendra.kt@...ux.vnet.ibm.com, edumazet@...gle.com, kuznet@....inr.ac.ru, jmorris@...ei.org, yoshfuji@...ux-ipv6.org, kaber@...sh.net, jiri@...nulli.us, hannes@...essinduktion.org, tom@...bertland.com, azhou@...ira.com, ebiederm@...ssion.com, ipm@...rality.org.uk, nicolas.dichtel@...nd.com, serge.hallyn@...onical.com, netdev@...r.kernel.org, linux-kernel@...r.kernel.org, anton@....ibm.com, nacc@...ux.vnet.ibm.com, srikar@...ux.vnet.ibm.com Subject: Re: [PATCH RFC V2 2/2] net: Optimize snmp stat aggregation by walking all the percpu data at once On Fri, 2015-08-28 at 11:24 -0700, David Miller wrote: > From: Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com> > Date: Fri, 28 Aug 2015 12:09:52 +0530 > > > On 08/28/2015 12:08 AM, David Miller wrote: > >> From: Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com> > >> Date: Wed, 26 Aug 2015 23:07:33 +0530 > >> > >>> @@ -4641,10 +4647,12 @@ static inline void __snmp6_fill_stats64(u64 > >>> *stats, void __percpu *mib, > >>> static void snmp6_fill_stats(u64 *stats, struct inet6_dev *idev, int > >>> attrtype, > >>> int bytes) > >>> { > >>> + u64 buff[IPSTATS_MIB_MAX] = {0,}; > >>> + > ... > > hope you wanted to know the overhead than to change the current > > patch. please let me know.. > > I want you to change that variable initializer to an explicit memset(). > > The compiler is emitting a memset() or similar _anyways_. > > Not because it will have any impact at all upon performance, but because > of how it looks to people trying to read and understand the code. I don't read it as particularly different. There are > 100 uses of the not quite a memset initialization style using "= { <0,> }" in net/ $ git grep -E "=\s*\{\s*0?\s*,?\s*\}" net | wc -l 138 There is a difference though if a struct is copied to user-space as a {} initialization only guarantees that struct members are initialized to 0 where memset also zeros any alignment padding. Maybe a checkpatch rule like this? --- scripts/checkpatch.pl | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl index e14dcdb..f79e5c9 100755 --- a/scripts/checkpatch.pl +++ b/scripts/checkpatch.pl @@ -3237,6 +3237,13 @@ sub process { next; } +# check for non-global initializations that could be memset + if ($realfile =~ m@^(drivers/net/|net/)@ && + $sline =~ /^.\s+$Declare\s*$Ident\s*=\s*\{\s*0?\s*,?\s*\}/) { + CHK("BRACE_INITIALIZATION", + "Prefer an explicit memset to a declaration initialization\n" . $herecurr); + } + # check for initialisation to aggregates open brace on the next line if ($line =~ /^.\s*{/ && $prevline =~ /(?:^|[^=])=\s*$/) { -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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