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b4f501916c
__get_cpu_var() is used for multiple purposes in the kernel source. One of
them is address calculation via the form &__get_cpu_var(x). This calculates
the address for the instance of the percpu variable of the current processor
based on an offset.
Other use cases are for storing and retrieving data from the current
processors percpu area. __get_cpu_var() can be used as an lvalue when
writing data or on the right side of an assignment.
__get_cpu_var() is defined as :
#define __get_cpu_var(var) (*this_cpu_ptr(&(var)))
__get_cpu_var() always only does an address determination. However, store
and retrieve operations could use a segment prefix (or global register on
other platforms) to avoid the address calculation.
this_cpu_write() and this_cpu_read() can directly take an offset into a
percpu area and use optimized assembly code to read and write per cpu
variables.
This patch converts __get_cpu_var into either an explicit address
calculation using this_cpu_ptr() or into a use of this_cpu operations that
use the offset. Thereby address calculations are avoided and less registers
are used when code is generated.
At the end of the patch set all uses of __get_cpu_var have been removed so
the macro is removed too.
The patch set includes passes over all arches as well. Once these operations
are used throughout then specialized macros can be defined in non -x86
arches as well in order to optimize per cpu access by f.e. using a global
register that may be set to the per cpu base.
Transformations done to __get_cpu_var()
1. Determine the address of the percpu instance of the current processor.
DEFINE_PER_CPU(int, y);
int *x = &__get_cpu_var(y);
Converts to
int *x = this_cpu_ptr(&y);
2. Same as #1 but this time an array structure is involved.
DEFINE_PER_CPU(int, y[20]);
int *x = __get_cpu_var(y);
Converts to
int *x = this_cpu_ptr(y);
3. Retrieve the content of the current processors instance of a per cpu
variable.
DEFINE_PER_CPU(int, y);
int x = __get_cpu_var(y)
Converts to
int x = __this_cpu_read(y);
4. Retrieve the content of a percpu struct
DEFINE_PER_CPU(struct mystruct, y);
struct mystruct x = __get_cpu_var(y);
Converts to
memcpy(&x, this_cpu_ptr(&y), sizeof(x));
5. Assignment to a per cpu variable
DEFINE_PER_CPU(int, y)
__get_cpu_var(y) = x;
Converts to
__this_cpu_write(y, x);
6. Increment/Decrement etc of a per cpu variable
DEFINE_PER_CPU(int, y);
__get_cpu_var(y)++
Converts to
__this_cpu_inc(y)
Acked-by: Chris Metcalf <cmetcalf@tilera.com>
Signed-off-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
117 lines
3.1 KiB
C
117 lines
3.1 KiB
C
/*
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* Copyright 2010 Tilera Corporation. All Rights Reserved.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation, version 2.
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
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* NON INFRINGEMENT. See the GNU General Public License for
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* more details.
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*/
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#include <linux/percpu.h>
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#include <linux/smp.h>
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#include <linux/hardirq.h>
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#include <linux/ptrace.h>
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#include <asm/hv_driver.h>
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#include <asm/irq_regs.h>
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#include <asm/traps.h>
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#include <hv/hypervisor.h>
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#include <arch/interrupts.h>
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/* All messages are stored here */
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static DEFINE_PER_CPU(HV_MsgState, msg_state);
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void init_messaging(void)
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{
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/* Allocate storage for messages in kernel space */
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HV_MsgState *state = this_cpu_ptr(&msg_state);
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int rc = hv_register_message_state(state);
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if (rc != HV_OK)
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panic("hv_register_message_state: error %d", rc);
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/* Make sure downcall interrupts will be enabled. */
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arch_local_irq_unmask(INT_INTCTRL_K);
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}
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void hv_message_intr(struct pt_regs *regs, int intnum)
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{
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/*
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* We enter with interrupts disabled and leave them disabled,
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* to match expectations of called functions (e.g.
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* do_ccupdate_local() in mm/slab.c). This is also consistent
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* with normal call entry for device interrupts.
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*/
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int message[HV_MAX_MESSAGE_SIZE/sizeof(int)];
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HV_RcvMsgInfo rmi;
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int nmsgs = 0;
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/* Track time spent here in an interrupt context */
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struct pt_regs *old_regs = set_irq_regs(regs);
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irq_enter();
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#ifdef CONFIG_DEBUG_STACKOVERFLOW
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/* Debugging check for stack overflow: less than 1/8th stack free? */
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{
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long sp = stack_pointer - (long) current_thread_info();
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if (unlikely(sp < (sizeof(struct thread_info) + STACK_WARN))) {
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pr_emerg("hv_message_intr: "
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"stack overflow: %ld\n",
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sp - sizeof(struct thread_info));
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dump_stack();
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}
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}
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#endif
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while (1) {
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HV_MsgState *state = this_cpu_ptr(&msg_state);
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rmi = hv_receive_message(*state, (HV_VirtAddr) message,
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sizeof(message));
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if (rmi.msglen == 0)
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break;
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if (rmi.msglen < 0)
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panic("hv_receive_message failed: %d", rmi.msglen);
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++nmsgs;
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if (rmi.source == HV_MSG_TILE) {
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int tag;
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/* we just send tags for now */
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BUG_ON(rmi.msglen != sizeof(int));
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tag = message[0];
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#ifdef CONFIG_SMP
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evaluate_message(message[0]);
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#else
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panic("Received IPI message %d in UP mode", tag);
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#endif
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} else if (rmi.source == HV_MSG_INTR) {
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HV_IntrMsg *him = (HV_IntrMsg *)message;
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struct hv_driver_cb *cb =
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(struct hv_driver_cb *)him->intarg;
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cb->callback(cb, him->intdata);
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__this_cpu_inc(irq_stat.irq_hv_msg_count);
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}
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}
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/*
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* We shouldn't have gotten a message downcall with no
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* messages available.
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*/
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if (nmsgs == 0)
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panic("Message downcall invoked with no messages!");
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/*
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* Track time spent against the current process again and
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* process any softirqs if they are waiting.
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*/
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irq_exit();
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set_irq_regs(old_regs);
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}
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