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Date: Thu, 7 Sep 2017 10:29:32 -0400
From: Prarit Bhargava <prarit@...hat.com>
To: Andi Kleen <andi@...stfloor.org>, x86@...nel.org
Cc: kan.liang@...el.com, peterz@...radead.org,
linux-kernel@...r.kernel.org, Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 2/2] x86/topology: Avoid wasting 128k for package id array
On 09/06/2017 07:17 PM, Andi Kleen wrote:
> From: Andi Kleen <ak@...ux.intel.com>
>
> I was looking at large early boot allocations and noticed that
> since (1f12e32f x86/topology: Create logical package id)
> every 64bit system allocates a 128k array to convert logical
> package ids.
>
> This happens because the array is sized for
> MAX_LOCAL_APIC and that is always 32k on 64bit systems,
> and it needs 4 bytes for each entry.
>
> This is fairly wasteful, especially for the common case
> of having only one socket, where we need 128K just to store
> a single 4 byte value.
>
> The max logical APIC value is not known at this point,
> so it's hard to size it correctly.
>
> The previous patch converted the only performance critical
> user to cache the value, and all others are fairly
> slow path, so we can just convert the O(1) array
> lookup to a linear search in cpu_data()
>
> This can also avoid the need for an extra bitmap structure
> to know if the logical package ID is already allocated.
> We can also save this information in cpu_data and look it
> up during the search.
>
> This patch removes the explicit arrays and replaces
> the lookups with explicit searches.
>
> Overall the new code is somewhat simpler, and needs a lot
> less run time memory.
>
> arch/x86/include/asm/processor.h | 6 +++++-
> arch/x86/kernel/smpboot.c | 47 ++++++++++++++++-------------------------------
> 2 files changed, 21 insertions(+), 32 deletions(-)
>
> The naming of the variables in cpu_data is still not
> great (_proc sometimes means package and sometimes means
> logical processor), but I followed the existing (messy)
> conventions when possible. At some point would be probably good
> to clean this up too.
>
> Tested on a 2S system, but it would be good
> to test on more obscure systems which may have problems
> with package IDs. I'm copying Prarit who had problematic systems
> before.
>
> Signed-off-by: Andi Kleen <ak@...ux.intel.com>
> ---
> arch/x86/include/asm/processor.h | 6 ++++-
> arch/x86/kernel/smpboot.c | 47 ++++++++++++++--------------------------
> 2 files changed, 21 insertions(+), 32 deletions(-)
>
> diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
> index 3fa26a61eabc..d369d2a82d8f 100644
> --- a/arch/x86/include/asm/processor.h
> +++ b/arch/x86/include/asm/processor.h
> @@ -124,13 +124,17 @@ struct cpuinfo_x86 {
> u16 booted_cores;
> /* Physical processor id: */
> u16 phys_proc_id;
> - /* Logical processor id: */
> + /* Logical processor (package) id: */
> u16 logical_proc_id;
> + /* Physical package ID */
> + u16 phys_pkg_id;
> /* Core id: */
> u16 cpu_core_id;
> /* Index into per_cpu list: */
> u16 cpu_index;
> u32 microcode;
> + /* Flags */
> + unsigned logical_proc_set : 1;
> } __randomize_layout;
>
> struct cpuid_regs {
> diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
> index 54b9e89d4d6b..e78460aeca0a 100644
> --- a/arch/x86/kernel/smpboot.c
> +++ b/arch/x86/kernel/smpboot.c
> @@ -100,9 +100,6 @@ DEFINE_PER_CPU_READ_MOSTLY(struct cpuinfo_x86, cpu_info);
> EXPORT_PER_CPU_SYMBOL(cpu_info);
>
> /* Logical package management. We might want to allocate that dynamically */
> -static int *physical_to_logical_pkg __read_mostly;
> -static unsigned long *physical_package_map __read_mostly;;
> -static unsigned int max_physical_pkg_id __read_mostly;
> unsigned int __max_logical_packages __read_mostly;
> EXPORT_SYMBOL(__max_logical_packages);
> static unsigned int logical_packages __read_mostly;
> @@ -282,17 +279,12 @@ static void notrace start_secondary(void *unused)
> */
> int topology_update_package_map(unsigned int pkg, unsigned int cpu)
> {
> - unsigned int new;
> + int new;
>
> - /* Called from early boot ? */
> - if (!physical_package_map)
> - return 0;
>
> - if (pkg >= max_physical_pkg_id)
> - return -EINVAL;
> -
> - /* Set the logical package id */
> - if (test_and_set_bit(pkg, physical_package_map))
> + /* Already available somewhere? */
> + new = topology_phys_to_logical_pkg(pkg);
> + if (new >= 0)
> goto found;
>
> if (logical_packages >= __max_logical_packages) {
> @@ -306,10 +298,11 @@ int topology_update_package_map(unsigned int pkg, unsigned int cpu)
> pr_info("CPU %u Converting physical %u to logical package %u\n",
> cpu, pkg, new);
> }
> - physical_to_logical_pkg[pkg] = new;
>
> found:
> - cpu_data(cpu).logical_proc_id = physical_to_logical_pkg[pkg];
> + cpu_data(cpu).phys_pkg_id = pkg;
> + cpu_data(cpu).logical_proc_id = new;
> + cpu_data(cpu).logical_proc_set = 1;
> return 0;
> }
>
> @@ -320,16 +313,21 @@ int topology_update_package_map(unsigned int pkg, unsigned int cpu)
> */
> int topology_phys_to_logical_pkg(unsigned int phys_pkg)
> {
> - if (phys_pkg >= max_physical_pkg_id)
> - return -1;
> - return physical_to_logical_pkg[phys_pkg];
> + int cpu;
> +
> + for_each_possible_cpu (cpu) {
> + if (cpu_data(cpu).phys_pkg_id == phys_pkg &&
> + cpu_data(cpu).logical_proc_set) {
> + return cpu_data(cpu).logical_proc_id;
> + }
> + }
> + return -1;
> }
> EXPORT_SYMBOL(topology_phys_to_logical_pkg);
>
> static void __init smp_init_package_map(struct cpuinfo_x86 *c, unsigned int cpu)
> {
> unsigned int ncpus;
> - size_t size;
>
> /*
> * Today neither Intel nor AMD support heterogenous systems. That
> @@ -362,19 +360,6 @@ static void __init smp_init_package_map(struct cpuinfo_x86 *c, unsigned int cpu)
> __max_logical_packages = DIV_ROUND_UP(total_cpus, ncpus);
> logical_packages = 0;
>
> - /*
> - * Possibly larger than what we need as the number of apic ids per
> - * package can be smaller than the actual used apic ids.
> - */
> - max_physical_pkg_id = DIV_ROUND_UP(MAX_LOCAL_APIC, ncpus);
> - size = max_physical_pkg_id * sizeof(unsigned int);
> - physical_to_logical_pkg = kmalloc(size, GFP_KERNEL);
> - memset(physical_to_logical_pkg, 0xff, size);
> - size = BITS_TO_LONGS(max_physical_pkg_id) * sizeof(unsigned long);
> - physical_package_map = kzalloc(size, GFP_KERNEL);
> -
> - pr_info("Max logical packages: %u\n", __max_logical_packages);
^^ This pr_info needs to stay IMO. ... testing now.
P.
> -
> topology_update_package_map(c->phys_proc_id, cpu);
> }
>
>
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