From 8d738ccbbc809e48916ac69c439d91986204565e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?J=C3=A9r=C3=A9my=20Zurcher?= <jeremy@asynk.ch>
Date: Thu, 7 Jan 2010 18:12:43 +0100
Subject: faster with a constant backoff and timespec struct as local function
 variable

---
 lf_ring_buffer.c      | 32 ++++++++++----------------------
 lf_ring_buffer.h      |  9 ---------
 lf_ring_buffer_test.c |  2 ++
 3 files changed, 12 insertions(+), 31 deletions(-)

diff --git a/lf_ring_buffer.c b/lf_ring_buffer.c
index 30532fc..506b0af 100644
--- a/lf_ring_buffer.c
+++ b/lf_ring_buffer.c
@@ -62,6 +62,8 @@
     #define _LOG_( ... )
 #endif
 
+#define BACKOFF_NANO_SLEEP  100
+
 /* initialize an empty lf_ring_buffer struct */
 lf_ring_buffer_t* lf_ring_buffer_create( size_t n_buf ) {
     /* alloc ring_buffer struct */
@@ -77,8 +79,6 @@ lf_ring_buffer_t* lf_ring_buffer_create( size_t n_buf ) {
     r->n_buf = n_buf;
     r->read_from = -1;
     r->write_to = 0;
-    r->write_delay = BACKOFF_DELAY_INIT;
-    r->read_delay = BACKOFF_DELAY_INIT;
     return r;
 }
 
@@ -91,8 +91,7 @@ void lf_ring_buffer_destroy( lf_ring_buffer_t *r ) {
 /* write data into the ring buffer */
 int lf_ring_buffer_write( lf_ring_buffer_t *r, void *data, int flags ) {
     int idx, next;
-    struct timespec st;
-    st.tv_sec=0;
+    struct timespec backoff;
     /* reserve a buffer */
     for(;;){
         idx = r->write_to;
@@ -117,11 +116,9 @@ int lf_ring_buffer_write( lf_ring_buffer_t *r, void *data, int flags ) {
         } else {
             _LOG_("write: not available\n");
             if(IS_NOT_BLOCKING(flags)) return -1;
-            st.tv_nsec=r->write_delay;
-            nanosleep(&st,NULL);
-            if( !(BACKOFF_INC_NOT(flags)) ) {
-                if(r->write_delay<BACKOFF_DELAY_MAX) r->write_delay+=BACKOFF_DELAY_INC;
-            }
+            backoff.tv_sec = 0;
+            backoff.tv_nsec = BACKOFF_NANO_SLEEP;
+            nanosleep(&backoff,NULL);
         }
     }
     /* try to set read_from on idx if it has not been initialized yet
@@ -134,17 +131,13 @@ int lf_ring_buffer_write( lf_ring_buffer_t *r, void *data, int flags ) {
     /* fill this buffer and mark it as filled */
     memcpy( r->buffer[idx].data, data, LFRB_DATA_SIZE );
     LFRB_MARK_AS_FILLED( r->buffer[idx] );
-    if( !(BACKOFF_INC_NOT(flags)) ) {
-        if(r->write_delay>BACKOFF_DELAY_INIT) r->write_delay-=BACKOFF_DELAY_INC;
-    }
     return 0;
 }
 
 /* read data from the ring buffer */
 int lf_ring_buffer_read( lf_ring_buffer_t *r, void *data, int flags ) {
     int idx, next;
-    struct timespec st;
-    st.tv_sec=0;
+    struct timespec backoff;
     if(r->read_from==-1) return -1;
     for(;;) {
         idx = r->read_from;
@@ -165,18 +158,13 @@ int lf_ring_buffer_read( lf_ring_buffer_t *r, void *data, int flags ) {
         } else { 
             _LOG_("read: not available\n");
             if(IS_NOT_BLOCKING(flags)) return -1;
-            st.tv_nsec=r->read_delay;
-            nanosleep(&st,NULL);
-            if( !(BACKOFF_INC_NOT(flags)) ) {
-                if(r->read_delay<BACKOFF_DELAY_MAX) r->read_delay+=BACKOFF_DELAY_INC;
-            }
+            backoff.tv_sec = 0;
+            backoff.tv_nsec = BACKOFF_NANO_SLEEP;
+            nanosleep(&backoff,NULL);
         }
     }
     /* finish the read process */
     LFRB_MARK_AS_READ( r->buffer[idx] );
-    if( !(BACKOFF_INC_NOT(flags)) ) {
-        if(r->read_delay>BACKOFF_DELAY_INIT) r->read_delay-=BACKOFF_DELAY_INC;
-    }
     return 0;
 }
 
diff --git a/lf_ring_buffer.h b/lf_ring_buffer.h
index 51d29e5..64bed4c 100644
--- a/lf_ring_buffer.h
+++ b/lf_ring_buffer.h
@@ -35,23 +35,14 @@ extern "C" {
 #include <sys/types.h>
 #include "lf_ring_buffer_data.h"
 
-#define BACKOFF_DELAY_INIT  100
-#define BACKOFF_DELAY_INC   100
-#define BACKOFF_DELAY_MAX   1000
-
 #define LFRB_NO_BLOCK   1       /* if buffer is full, leave instead of try again and again */
 #define IS_NOT_BLOCKING( flags ) ( (flags)&LFRB_NO_BLOCK )
 
-#define LFRB_NO_BACKOFF_INC     2       /* do not use BACKOFF_DELAY_X */
-#define BACKOFF_INC_NOT( flags ) ( (flags)&LFRB_NO_BACKOFF_INC )
-
 typedef struct ring_buffer {
     LFRB_BUFFER_TYPE *buffer;   /* buffer data */
     size_t n_buf;               /* number of buffers */
     int read_from;              /* index where to read data from */
     int write_to;               /* index where to write data to */
-    int write_delay;            /* backoff nanosleep to reduce fast looping when writing */
-    int read_delay;             /* backoff nanosleep to reduce fast looping when reading */
 } lf_ring_buffer_t;
 
 /* return an initialized lf_ring_buffer_t struct */
diff --git a/lf_ring_buffer_test.c b/lf_ring_buffer_test.c
index b3ec016..b7a7d30 100644
--- a/lf_ring_buffer_test.c
+++ b/lf_ring_buffer_test.c
@@ -138,12 +138,14 @@ int main( int argc, char** argv ) {
         printf("parallel blocking read operations ...\n");
         sequential_reads( ring, b_len, 0 );
     }
+    /*
     for(i=5; i<=100;i*=22) {
         printf("%d parallel blocking with no backoff inc write operations .... \n",i);
         parallel_writes( i, ring, b_len, LFRB_NO_BACKOFF_INC );
         printf("parallel blocking read operations ...\n");
         sequential_reads( ring, b_len, LFRB_NO_BACKOFF_INC );
     }
+    */
     for(i=5; i<=100;i*=22) {
         printf("%d parallel non blocking write operations .... \n",i);
         parallel_writes( i, ring, b_len, LFRB_NO_BLOCK );
-- 
cgit v1.1-2-g2b99