Andrew Morton a écrit :
Ravikiran G Thirumalai <[email protected]> wrote:
On Fri, Jan 27, 2006 at 09:53:53AM +0100, Eric Dumazet wrote:
Ravikiran G Thirumalai a écrit :
Change the atomic_t sockets_allocated member of struct proto to a
per-cpu counter.
Signed-off-by: Pravin B. Shelar <[email protected]>
Signed-off-by: Ravikiran Thirumalai <[email protected]>
Signed-off-by: Shai Fultheim <[email protected]>
Hi Ravikiran
If I correctly read this patch, I think there is a scalability problem.
On a big SMP machine, read_sockets_allocated() is going to be a real killer.
Say we have 128 Opterons CPUS in a box.
read_sockets_allocated is being invoked when when /proc/net/protocols is read,
which can be assumed as not frequent.
At sk_stream_mem_schedule(), read_sockets_allocated() is invoked only
certain conditions, under memory pressure -- on a large CPU count machine,
you'd have large memory, and I don't think read_sockets_allocated would get
called often. It did not atleast on our 8cpu/16G box. So this should be OK
I think.
That being said, the percpu_counters aren't a terribly successful concept
and probably do need a revisit due to the high inaccuracy at high CPU
counts. It might be better to do some generic version of vm_acct_memory()
instead.
There are several issues here :
alloc_percpu() current implementation is a a waste of ram. (because it uses
slab allocations that have a minimum size of 32 bytes)
Currently we cannot use per_cpu(&some_object, cpu), so a generic version of
vm_acct_memory() would need a rework of percpu.h and maybe this is not
possible on every platform ?
#define per_cpu(var, cpu) (*RELOC_HIDE(&per_cpu__##var, __per_cpu_offset[cpu]))
-->
#define per_cpu_name(var) per_cpu__##var
#define per_cpu_addr(var) &per_cpu_name(var)
#define per_cpu(var, cpu) (*RELOC_HIDE(per_cpu_addr(var), __per_cpu_offset[cpu])
But this could render TLS migration difficult...
Eric
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