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Message-ID: <1439909185.6443.18.camel@edumazet-glaptop2.roam.corp.google.com> Date: Tue, 18 Aug 2015 07:46:25 -0700 From: Eric Dumazet <eric.dumazet@...il.com> To: Christophe Leroy <christophe.leroy@....fr> Cc: "David S. Miller" <davem@...emloft.net>, Alexey Kuznetsov <kuznet@....inr.ac.ru>, James Morris <jmorris@...ei.org>, Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>, Patrick McHardy <kaber@...sh.net>, netdev@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH] net: ipv4: inlining ip_send_check() On Tue, 2015-08-18 at 14:14 +0200, Christophe Leroy wrote: > ip_send_check() is a function that does nothing but calling > ip_fast_csum() after having zeroed iph->check > > We get (on PPC) a quite long function for just that, as it requires > setting the stack frame, saving volatile regs, restoring them after > the call, etc ... > > c02d3e3c <ip_send_check>: > c02d3e3c: 7c 08 02 a6 mflr r0 > c02d3e40: 94 21 ff f0 stwu r1,-16(r1) > c02d3e44: 39 20 00 00 li r9,0 > c02d3e48: 93 e1 00 0c stw r31,12(r1) > c02d3e4c: 90 01 00 14 stw r0,20(r1) > c02d3e50: b1 23 00 0a sth r9,10(r3) > c02d3e54: 88 83 00 00 lbz r4,0(r3) > c02d3e58: 7c 7f 1b 78 mr r31,r3 > c02d3e5c: 54 84 07 3e clrlwi r4,r4,28 > c02d3e60: 4b d3 ab 7d bl c000e9dc <ip_fast_csum> > c02d3e64: b0 7f 00 0a sth r3,10(r31) > c02d3e68: 80 01 00 14 lwz r0,20(r1) > c02d3e6c: 83 e1 00 0c lwz r31,12(r1) > c02d3e70: 7c 08 03 a6 mtlr r0 > c02d3e74: 38 21 00 10 addi r1,r1,16 > c02d3e78: 4e 80 00 20 blr That's because you should inline ip_fast_csum() instead. We do not want to inline ip_send_check() on eg x86, as it is clearly too long. ffffffff816d72e0 <ip_send_check>: ffffffff816d72e0: e8 9b e3 0c 00 callq ffffffff817a5680 <__fentry__> ffffffff816d72e5: 0f b6 17 movzbl (%rdi),%edx ffffffff816d72e8: 55 push %rbp ffffffff816d72e9: 31 c0 xor %eax,%eax ffffffff816d72eb: 66 89 47 0a mov %ax,0xa(%rdi) ffffffff816d72ef: 48 89 f8 mov %rdi,%rax ffffffff816d72f2: 48 89 e5 mov %rsp,%rbp ffffffff816d72f5: 83 e2 0f and $0xf,%edx ffffffff816d72f8: 8b 08 mov (%rax),%ecx ffffffff816d72fa: 83 ea 04 sub $0x4,%edx ffffffff816d72fd: 76 24 jbe ffffffff816d7323 <ip_send_check+0x43> ffffffff816d72ff: 03 48 04 add 0x4(%rax),%ecx ffffffff816d7302: 13 48 08 adc 0x8(%rax),%ecx ffffffff816d7305: 13 48 0c adc 0xc(%rax),%ecx ffffffff816d7308: 13 48 10 adc 0x10(%rax),%ecx ffffffff816d730b: 48 8d 40 04 lea 0x4(%rax),%rax ffffffff816d730f: ff ca dec %edx ffffffff816d7311: 75 f5 jne ffffffff816d7308 <ip_send_check+0x28> ffffffff816d7313: 83 d1 00 adc $0x0,%ecx ffffffff816d7316: 89 ca mov %ecx,%edx ffffffff816d7318: c1 e9 10 shr $0x10,%ecx ffffffff816d731b: 66 01 d1 add %dx,%cx ffffffff816d731e: 83 d1 00 adc $0x0,%ecx ffffffff816d7321: f7 d1 not %ecx ffffffff816d7323: 66 89 4f 0a mov %cx,0xa(%rdi) ffffffff816d7327: 5d pop %rbp ffffffff816d7328: c3 retq -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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