| Message ID | 1446203414-4013-20-git-send-email-kraxel@redhat.com |
|---|---|
| State | New |
| Headers | show |
On Fri, Oct 30, 2015 at 12:10:14PM +0100, Gerd Hoffmann wrote: > From: Peter Lieven <pl@kamp.de> > > the idea behind this patch is to allow the buffer to shrink, but > make this a seldom operation. The buffers average size is measured > exponentionally smoothed with am alpha of 1/128. s/am/an/ > > Signed-off-by: Peter Lieven <pl@kamp.de> > Signed-off-by: Gerd Hoffmann <kraxel@redhat.com> > --- > include/qemu/buffer.h | 1 + > util/buffer.c | 34 ++++++++++++++++++++++++++++------ > 2 files changed, 29 insertions(+), 6 deletions(-) > diff --git a/util/buffer.c b/util/buffer.c > index fe5a44e..5461f86 100644 > --- a/util/buffer.c > +++ b/util/buffer.c > @@ -23,6 +23,7 @@ > > #define BUFFER_MIN_INIT_SIZE 4096 > #define BUFFER_MIN_SHRINK_SIZE 65536 > +#define BUFFER_AVG_SIZE_SHIFT 7 > > static size_t buffer_req_size(Buffer *buffer, size_t len) > { > @@ -37,6 +38,11 @@ static void buffer_adj_size(Buffer *buffer, size_t len) > buffer->buffer = g_realloc(buffer->buffer, buffer->capacity); > trace_buffer_resize(buffer->name ?: "unnamed", > old, buffer->capacity); > + > + /* make it even harder for the buffer to shrink, reset average size > + * to currenty capacity if it is larger than the average. */ s/currenty/current/ Reviewed-by: Daniel P. Berrange <berrange@redhat.com> Regards, Daniel
Am 30.10.2015 um 12:10 schrieb Gerd Hoffmann: > From: Peter Lieven <pl@kamp.de> > > the idea behind this patch is to allow the buffer to shrink, but > make this a seldom operation. The buffers average size is measured > exponentionally smoothed with am alpha of 1/128. > > Signed-off-by: Peter Lieven <pl@kamp.de> > Signed-off-by: Gerd Hoffmann <kraxel@redhat.com> > --- > include/qemu/buffer.h | 1 + > util/buffer.c | 34 ++++++++++++++++++++++++++++------ > 2 files changed, 29 insertions(+), 6 deletions(-) > > diff --git a/include/qemu/buffer.h b/include/qemu/buffer.h > index 0a69b3a..dead9b7 100644 > --- a/include/qemu/buffer.h > +++ b/include/qemu/buffer.h > @@ -37,6 +37,7 @@ struct Buffer { > char *name; > size_t capacity; > size_t offset; > + uint64_t avg_size; > uint8_t *buffer; > }; > > diff --git a/util/buffer.c b/util/buffer.c > index fe5a44e..5461f86 100644 > --- a/util/buffer.c > +++ b/util/buffer.c > @@ -23,6 +23,7 @@ > > #define BUFFER_MIN_INIT_SIZE 4096 > #define BUFFER_MIN_SHRINK_SIZE 65536 > +#define BUFFER_AVG_SIZE_SHIFT 7 > > static size_t buffer_req_size(Buffer *buffer, size_t len) > { > @@ -37,6 +38,11 @@ static void buffer_adj_size(Buffer *buffer, size_t len) > buffer->buffer = g_realloc(buffer->buffer, buffer->capacity); > trace_buffer_resize(buffer->name ?: "unnamed", > old, buffer->capacity); > + > + /* make it even harder for the buffer to shrink, reset average size > + * to currenty capacity if it is larger than the average. */ > + buffer->avg_size = MAX(buffer->avg_size, > + buffer->capacity << BUFFER_AVG_SIZE_SHIFT); > } > > void buffer_init(Buffer *buffer, const char *name, ...) > @@ -48,16 +54,30 @@ void buffer_init(Buffer *buffer, const char *name, ...) > va_end(ap); > } > > +static uint64_t buffer_get_avg_size(Buffer *buffer) > +{ > + return buffer->avg_size >> BUFFER_AVG_SIZE_SHIFT; > +} > + > void buffer_shrink(Buffer *buffer) > { > - /* > - * Only shrink in case the used size is *much* smaller than the > - * capacity, to avoid bumping up & down the buffers all the time. > + size_t new; > + > + /* Calculate the average size of the buffer as > + * avg_size = avg_size * ( 1 - a ) + required_size * a > + * where a is 1 / 2 ^ QIO_BUFFER_AVG_SIZE_SHIFT. */ > + buffer->avg_size *= (1 << BUFFER_AVG_SIZE_SHIFT) - 1; > + buffer->avg_size >>= BUFFER_AVG_SIZE_SHIFT; > + buffer->avg_size += buffer_req_size(buffer, 0); > + > + /* And then only shrink if the average size of the buffer is much > + * too big, to avoid bumping up & down the buffers all the time. > * realloc() isn't exactly cheap ... > */ > - if (buffer->offset < (buffer->capacity >> 3) && > - buffer->capacity > BUFFER_MIN_SHRINK_SIZE) { > - return; > + new = buffer_req_size(buffer, buffer_get_avg_size(buffer)); > + if (new < buffer->capacity >> 3 && > + new >= BUFFER_MIN_SHRINK_SIZE) { > + buffer_adj_size(buffer, buffer_get_avg_size(buffer)); > } > > buffer_adj_size(buffer, 0); > @@ -83,6 +103,7 @@ uint8_t *buffer_end(Buffer *buffer) > void buffer_reset(Buffer *buffer) > { > buffer->offset = 0; > + buffer_shrink(buffer); > } > > void buffer_free(Buffer *buffer) > @@ -107,6 +128,7 @@ void buffer_advance(Buffer *buffer, size_t len) > memmove(buffer->buffer, buffer->buffer + len, > (buffer->offset - len)); > buffer->offset -= len; > + buffer_shrink(buffer); > } > > void buffer_move_empty(Buffer *to, Buffer *from) This isn't the last version of this patch. Please have a look at: https://github.com/plieven/qemu/commit/e599748ab1ef381d4b1c88bf1ea1454dd89353fb Peter
diff --git a/include/qemu/buffer.h b/include/qemu/buffer.h index 0a69b3a..dead9b7 100644 --- a/include/qemu/buffer.h +++ b/include/qemu/buffer.h @@ -37,6 +37,7 @@ struct Buffer { char *name; size_t capacity; size_t offset; + uint64_t avg_size; uint8_t *buffer; }; diff --git a/util/buffer.c b/util/buffer.c index fe5a44e..5461f86 100644 --- a/util/buffer.c +++ b/util/buffer.c @@ -23,6 +23,7 @@ #define BUFFER_MIN_INIT_SIZE 4096 #define BUFFER_MIN_SHRINK_SIZE 65536 +#define BUFFER_AVG_SIZE_SHIFT 7 static size_t buffer_req_size(Buffer *buffer, size_t len) { @@ -37,6 +38,11 @@ static void buffer_adj_size(Buffer *buffer, size_t len) buffer->buffer = g_realloc(buffer->buffer, buffer->capacity); trace_buffer_resize(buffer->name ?: "unnamed", old, buffer->capacity); + + /* make it even harder for the buffer to shrink, reset average size + * to currenty capacity if it is larger than the average. */ + buffer->avg_size = MAX(buffer->avg_size, + buffer->capacity << BUFFER_AVG_SIZE_SHIFT); } void buffer_init(Buffer *buffer, const char *name, ...) @@ -48,16 +54,30 @@ void buffer_init(Buffer *buffer, const char *name, ...) va_end(ap); } +static uint64_t buffer_get_avg_size(Buffer *buffer) +{ + return buffer->avg_size >> BUFFER_AVG_SIZE_SHIFT; +} + void buffer_shrink(Buffer *buffer) { - /* - * Only shrink in case the used size is *much* smaller than the - * capacity, to avoid bumping up & down the buffers all the time. + size_t new; + + /* Calculate the average size of the buffer as + * avg_size = avg_size * ( 1 - a ) + required_size * a + * where a is 1 / 2 ^ QIO_BUFFER_AVG_SIZE_SHIFT. */ + buffer->avg_size *= (1 << BUFFER_AVG_SIZE_SHIFT) - 1; + buffer->avg_size >>= BUFFER_AVG_SIZE_SHIFT; + buffer->avg_size += buffer_req_size(buffer, 0); + + /* And then only shrink if the average size of the buffer is much + * too big, to avoid bumping up & down the buffers all the time. * realloc() isn't exactly cheap ... */ - if (buffer->offset < (buffer->capacity >> 3) && - buffer->capacity > BUFFER_MIN_SHRINK_SIZE) { - return; + new = buffer_req_size(buffer, buffer_get_avg_size(buffer)); + if (new < buffer->capacity >> 3 && + new >= BUFFER_MIN_SHRINK_SIZE) { + buffer_adj_size(buffer, buffer_get_avg_size(buffer)); } buffer_adj_size(buffer, 0); @@ -83,6 +103,7 @@ uint8_t *buffer_end(Buffer *buffer) void buffer_reset(Buffer *buffer) { buffer->offset = 0; + buffer_shrink(buffer); } void buffer_free(Buffer *buffer) @@ -107,6 +128,7 @@ void buffer_advance(Buffer *buffer, size_t len) memmove(buffer->buffer, buffer->buffer + len, (buffer->offset - len)); buffer->offset -= len; + buffer_shrink(buffer); } void buffer_move_empty(Buffer *to, Buffer *from)