[PATCH] Compact sk_stream_mem_schedule() code

[PATCH] Compact sk_stream_mem_schedule() code

[Pavel Emelyanov]

This function references sk->sk_prot->xxx for many times.
It turned out, that there's so many code in it, that gcc 
cannot always optimize access to sk->sk_prot's fields.

After saving the sk->sk_prot on the stack and comparing
disassembled code, it turned out that the function became
~10 bytes shorter and made less dereferences (on i386 and 
x86_64). Stack consumption didn't grow.

Besides, this patch drives most of this function into the
80 columns limit.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>

---

diff --git a/net/core/stream.c b/net/core/stream.c
index 755bacb..b2fb846 100644
--- a/net/core/stream.c
+++ b/net/core/stream.c
@@ -210,35 +210,36 @@ EXPORT_SYMBOL(__sk_stream_mem_reclaim);
 int sk_stream_mem_schedule(struct sock *sk, int size, int kind)
 {
 	int amt = sk_stream_pages(size);
+	struct proto *prot = sk->sk_prot;
 
 	sk->sk_forward_alloc += amt * SK_STREAM_MEM_QUANTUM;
-	atomic_add(amt, sk->sk_prot->memory_allocated);
+	atomic_add(amt, prot->memory_allocated);
 
 	/* Under limit. */
-	if (atomic_read(sk->sk_prot->memory_allocated) < sk->sk_prot->sysctl_mem[0]) {
-		if (*sk->sk_prot->memory_pressure)
-			*sk->sk_prot->memory_pressure = 0;
+	if (atomic_read(prot->memory_allocated) < prot->sysctl_mem[0]) {
+		if (*prot->memory_pressure)
+			*prot->memory_pressure = 0;
 		return 1;
 	}
 
 	/* Over hard limit. */
-	if (atomic_read(sk->sk_prot->memory_allocated) > sk->sk_prot->sysctl_mem[2]) {
-		sk->sk_prot->enter_memory_pressure();
+	if (atomic_read(prot->memory_allocated) > prot->sysctl_mem[2]) {
+		prot->enter_memory_pressure();
 		goto suppress_allocation;
 	}
 
 	/* Under pressure. */
-	if (atomic_read(sk->sk_prot->memory_allocated) > sk->sk_prot->sysctl_mem[1])
-		sk->sk_prot->enter_memory_pressure();
+	if (atomic_read(prot->memory_allocated) > prot->sysctl_mem[1])
+		prot->enter_memory_pressure();
 
 	if (kind) {
-		if (atomic_read(&sk->sk_rmem_alloc) < sk->sk_prot->sysctl_rmem[0])
+		if (atomic_read(&sk->sk_rmem_alloc) < prot->sysctl_rmem[0])
 			return 1;
-	} else if (sk->sk_wmem_queued < sk->sk_prot->sysctl_wmem[0])
+	} else if (sk->sk_wmem_queued < prot->sysctl_wmem[0])
 		return 1;
 
-	if (!*sk->sk_prot->memory_pressure ||
-	    sk->sk_prot->sysctl_mem[2] > atomic_read(sk->sk_prot->sockets_allocated) *
+	if (!*prot->memory_pressure ||
+	    prot->sysctl_mem[2] > atomic_read(prot->sockets_allocated) *
 				sk_stream_pages(sk->sk_wmem_queued +
 						atomic_read(&sk->sk_rmem_alloc) +
 						sk->sk_forward_alloc))
@@ -258,7 +259,7 @@ suppress_allocation:
 
 	/* Alas. Undo changes. */
 	sk->sk_forward_alloc -= amt * SK_STREAM_MEM_QUANTUM;
-	atomic_sub(amt, sk->sk_prot->memory_allocated);
+	atomic_sub(amt, prot->memory_allocated);
 	return 0;
 }
 

Re: [PATCH] Compact sk_stream_mem_schedule() code

[Arnaldo Carvalho de Melo]

Em Mon, Nov 19, 2007 at 03:13:44PM +0300, Pavel Emelyanov escreveu:
> This function references sk->sk_prot->xxx for many times.
> It turned out, that there's so many code in it, that gcc 
> cannot always optimize access to sk->sk_prot's fields.
> 
> After saving the sk->sk_prot on the stack and comparing
> disassembled code, it turned out that the function became
> ~10 bytes shorter and made less dereferences (on i386 and 
> x86_64). Stack consumption didn't grow.
> 
> Besides, this patch drives most of this function into the
> 80 columns limit.
> 
> Signed-off-by: Pavel Emelyanov <xemul@openvz.org>

I wonder if making it 'const struct proto *prot = sk->sk_prot;'

would make any difference.

Acked-by: Arnaldo Carvalho de Melo <acme@redhat.com>

Re: [PATCH] Compact sk_stream_mem_schedule() code

[David Miller]

From: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Date: Mon, 19 Nov 2007 17:30:59 -0200

> Em Mon, Nov 19, 2007 at 03:13:44PM +0300, Pavel Emelyanov escreveu:
> > This function references sk->sk_prot->xxx for many times.
> > It turned out, that there's so many code in it, that gcc 
> > cannot always optimize access to sk->sk_prot's fields.
> > 
> > After saving the sk->sk_prot on the stack and comparing
> > disassembled code, it turned out that the function became
> > ~10 bytes shorter and made less dereferences (on i386 and 
> > x86_64). Stack consumption didn't grow.
> > 
> > Besides, this patch drives most of this function into the
> > 80 columns limit.
> > 
> > Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
> 
> I wonder if making it 'const struct proto *prot = sk->sk_prot;'
> 
> would make any difference.

Such experiments are always useful, but I doubt there will
be substantial gains in this case.

> Acked-by: Arnaldo Carvalho de Melo <acme@redhat.com>

I've applied the patch, thanks Pavel.