remove put_cpu_no_resched() (8b0b1db0) · Commits · 戴 / test

put_cpu_no_resched() is an optimization of put_cpu() which unfortunately can cause high latencies. The nfs iostats code uses put_cpu_no_resched() in a code sequence where a reschedule request caused by an interrupt between the get_cpu() and the put_cpu_no_resched() can delay the reschedule for at least HZ. The other users of put_cpu_no_resched() optimize correctly in interrupt code, but there is no real harm in using the put_cpu() function which is an alias for preempt_enable(). The extra check of the preemmpt count is not as critical as the potential source of missing a reschedule. Debugged in the preempt-rt tree and verified in mainline. Impact: remove a high latency source [akpm@linux-foundation.org: build fix] Signed-off-by:

Thomas Gleixner <tglx@linutronix.de> Acked-by:

Ingo Molnar <mingo@elte.hu> Cc: Tony Luck <tony.luck@intel.com> Cc: Trond Myklebust <Trond.Myklebust@netapp.com> Cc: "J. Bruce Fields" <bfields@fieldses.org> Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

arch/ia64/kernel/perfmon.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -5595,7 +5595,7 @@ pfm_interrupt_handler(int irq, void *arg)
		(*pfm_alt_intr_handler->handler)(irq, arg, regs);
		}

		put_cpu_no_resched();
		put_cpu();
		return IRQ_HANDLED;
		}

fs/nfs/iostat.h

+3 −3

Original line number	Diff line number	Diff line
		@@ -31,7 +31,7 @@ static inline void nfs_inc_server_stats(const struct nfs_server *server,
		cpu = get_cpu();
		iostats = per_cpu_ptr(server->io_stats, cpu);
		iostats->events[stat]++;
		put_cpu_no_resched();
		put_cpu();
		}

		static inline void nfs_inc_stats(const struct inode *inode,
		@@ -50,7 +50,7 @@ static inline void nfs_add_server_stats(const struct nfs_server *server,
		cpu = get_cpu();
		iostats = per_cpu_ptr(server->io_stats, cpu);
		iostats->bytes[stat] += addend;
		put_cpu_no_resched();
		put_cpu();
		}

		static inline void nfs_add_stats(const struct inode *inode,
		@@ -71,7 +71,7 @@ static inline void nfs_add_fscache_stats(struct inode *inode,
		cpu = get_cpu();
		iostats = per_cpu_ptr(NFS_SERVER(inode)->io_stats, cpu);
		iostats->fscache[stat] += addend;
		put_cpu_no_resched();
		put_cpu();
		}
		#endif

include/linux/smp.h

+0 −1

Original line number	Diff line number	Diff line
		@@ -177,7 +177,6 @@ static inline void init_call_single_data(void)

		#define get_cpu() ({ preempt_disable(); smp_processor_id(); })
		#define put_cpu() preempt_enable()
		#define put_cpu_no_resched() preempt_enable_no_resched()

		/*
		* Callback to arch code if there's nosmp or maxcpus=0 on the

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