Re: 2.6.21-rc5-mm1

[Eric Dumazet]

Andrew Morton a écrit :
> The wheel spins around, slows then settles on.... 
> time-smp-friendly-alignment-of-struct-clocksource.patch!
>
> Presumably because the ____cacheline_aligned made vsyscall_gtod_data_t get
> too big.  Or something.

Very strange, since here I have plenty of available room (256 bytes) :

ffffffffff600000 T vgettimeofday
ffffffffff60004e t vsysc2
ffffffffff600140 t vread_hpet
ffffffffff600150 t vread_tsc
ffffffffff600180 D __vsyscall_gtod_data
ffffffffff600280 D __vgetcpu_mode
ffffffffff6002c0 D __jiffies
<lot of space (256 bytes)>
ffffffffff600400 T vtime
ffffffffff600413 t vsysc1
ffffffffff600800 T vgetcpu
ffffffffff600c00 T venosys_1

It must depends on the compiler, and/or CONFIG_XXX options...

Anyway, I think we can safely move __vgetcpu_mode & __jiffies to the 1024 
bytes area dedicated to vgetcpu() implementation. This saves 128 bytes from 
vsyscall_0 area.

Could we add this patch instead of dropping 
time-smp-friendly-alignment-of-struct-clocksource.patch ?

Thank you

[PATCH] x86_64 : move __vgetcpu_mode & __jiffies  to the vsyscall_2 zone

We apparently hit the 1024 limit of vsyscall_0 zone when some debugging 
options are set, or if __vsyscall_gtod_data is 64 bytes larger.

In order to save 128 bytes from the vsyscall_0 zone, we move __vgetcpu_mode & 
__jiffies to vsyscall_2 zone where they really belong, since they are used 
only from vgetcpu() (which is in this vsyscall_2 area).

After patch is applied, new layout is :

ffffffffff600000 T vgettimeofday
ffffffffff60004e t vsysc2
ffffffffff600140 t vread_hpet
ffffffffff600150 t vread_tsc
ffffffffff600180 D __vsyscall_gtod_data
ffffffffff600400 T vtime
ffffffffff600413 t vsysc1
ffffffffff600800 T vgetcpu
ffffffffff600870 D __vgetcpu_mode
ffffffffff600880 D __jiffies
ffffffffff600c00 T venosys_1


Signed-off-by: Eric Dumazet <dada1@xxxxxxxxxxxxx>
--- linux-2.6.21-rc5/arch/x86_64/kernel/vmlinux.lds.S
+++ linux-2.6.21-rc5-ed/arch/x86_64/kernel/vmlinux.lds.S
@@ -94,6 +94,12 @@ SECTIONS
 		{ *(.vsyscall_gtod_data) }
   vsyscall_gtod_data = VVIRT(.vsyscall_gtod_data);
 
+
+  .vsyscall_1 ADDR(.vsyscall_0) + 1024: AT(VLOAD(.vsyscall_1))
+		{ *(.vsyscall_1) }
+  .vsyscall_2 ADDR(.vsyscall_0) + 2048: AT(VLOAD(.vsyscall_2))
+		{ *(.vsyscall_2) }
+
   .vgetcpu_mode : AT(VLOAD(.vgetcpu_mode)) { *(.vgetcpu_mode) }
   vgetcpu_mode = VVIRT(.vgetcpu_mode);
 
@@ -101,10 +107,6 @@ SECTIONS
   .jiffies : AT(VLOAD(.jiffies)) { *(.jiffies) }
   jiffies = VVIRT(.jiffies);
 
-  .vsyscall_1 ADDR(.vsyscall_0) + 1024: AT(VLOAD(.vsyscall_1))
-		{ *(.vsyscall_1) }
-  .vsyscall_2 ADDR(.vsyscall_0) + 2048: AT(VLOAD(.vsyscall_2))
-		{ *(.vsyscall_2) }
   .vsyscall_3 ADDR(.vsyscall_0) + 3072: AT(VLOAD(.vsyscall_3))
 		{ *(.vsyscall_3) }