remove put_cpu_no_resched()

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

[[email protected]: build fix]
Signed-off-by: Thomas Gleixner <[email protected]>
Acked-by: Ingo Molnar <[email protected]>
Cc: Tony Luck <[email protected]>
Cc: Trond Myklebust <[email protected]>
Cc: "J. Bruce Fields" <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

diff --git a/arch/ia64/kernel/perfmon.c b/arch/ia64/kernel/perfmon.c
index 8a06dc480594c0d3e93636eccad9ea9316944127..bdc176cb5e85bc471649d47259951274db3c29e9 100644 (file)
--- a/arch/ia64/kernel/perfmon.c
+++ b/arch/ia64/kernel/perfmon.c
@@ -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;
 }
 

diff --git a/fs/nfs/iostat.h b/fs/nfs/iostat.h
index a2ab2529b5ca4ee1c1ac2b8e3889e4651bb8f1ac..ceda50aad73cc5a3bc93baeaaa7771ebd7a0f00f 100644 (file)
--- a/fs/nfs/iostat.h
+++ b/fs/nfs/iostat.h
@@ -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
 

diff --git a/include/linux/smp.h b/include/linux/smp.h
index a69db820eed6b33bfe71e6f946536209dd935372..9e3d8af09207c9ec5ecf58dbb6c0034200947158 100644 (file)
--- a/include/linux/smp.h
+++ b/include/linux/smp.h
@@ -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