[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 [EMAIL PROTECTED]

---

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;
 }
 
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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 [EMAIL PROTECTED]

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

would make any difference.

Acked-by: Arnaldo Carvalho de Melo [EMAIL PROTECTED]
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Re: [PATCH] Compact sk_stream_mem_schedule() code

[David Miller]

From: Arnaldo Carvalho de Melo [EMAIL PROTECTED]
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 [EMAIL PROTECTED]
 
 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 [EMAIL PROTECTED]

I've applied the patch, thanks Pavel.
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