Merge pull request #19339 from arjunroy/maybe_embiggen_v2

Reduced instruction count for maybe_embiggen common case.
pull/19345/head
Arjun Roy 6 years ago committed by GitHub
commit 2c4b32a599
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  1. 52
      src/core/lib/slice/slice_buffer.cc

@ -32,35 +32,45 @@
/* grow a buffer; requires GRPC_SLICE_BUFFER_INLINE_ELEMENTS > 1 */
#define GROW(x) (3 * (x) / 2)
/* Typically, we do not actually need to embiggen (by calling
* memmove/malloc/realloc) - only if we were up against the full capacity of the
* slice buffer. If do_embiggen is inlined, the compiler clobbers multiple
* registers pointlessly in the common case. */
static void GPR_ATTRIBUTE_NOINLINE do_embiggen(grpc_slice_buffer* sb,
const size_t slice_count,
const size_t slice_offset) {
if (slice_offset != 0) {
/* Make room by moving elements if there's still space unused */
memmove(sb->base_slices, sb->slices, sb->count * sizeof(grpc_slice));
sb->slices = sb->base_slices;
} else {
/* Allocate more memory if no more space is available */
const size_t new_capacity = GROW(sb->capacity);
sb->capacity = new_capacity;
if (sb->base_slices == sb->inlined) {
sb->base_slices = static_cast<grpc_slice*>(
gpr_malloc(new_capacity * sizeof(grpc_slice)));
memcpy(sb->base_slices, sb->inlined, slice_count * sizeof(grpc_slice));
} else {
sb->base_slices = static_cast<grpc_slice*>(
gpr_realloc(sb->base_slices, new_capacity * sizeof(grpc_slice)));
}
sb->slices = sb->base_slices + slice_offset;
}
}
static void maybe_embiggen(grpc_slice_buffer* sb) {
if (sb->count == 0) {
sb->slices = sb->base_slices;
return;
}
/* How far away from sb->base_slices is sb->slices pointer */
size_t slice_offset = static_cast<size_t>(sb->slices - sb->base_slices);
size_t slice_count = sb->count + slice_offset;
if (slice_count == sb->capacity) {
if (sb->base_slices != sb->slices) {
/* Make room by moving elements if there's still space unused */
memmove(sb->base_slices, sb->slices, sb->count * sizeof(grpc_slice));
sb->slices = sb->base_slices;
} else {
/* Allocate more memory if no more space is available */
sb->capacity = GROW(sb->capacity);
GPR_ASSERT(sb->capacity > slice_count);
if (sb->base_slices == sb->inlined) {
sb->base_slices = static_cast<grpc_slice*>(
gpr_malloc(sb->capacity * sizeof(grpc_slice)));
memcpy(sb->base_slices, sb->inlined, slice_count * sizeof(grpc_slice));
} else {
sb->base_slices = static_cast<grpc_slice*>(
gpr_realloc(sb->base_slices, sb->capacity * sizeof(grpc_slice)));
}
sb->slices = sb->base_slices + slice_offset;
}
if (GPR_UNLIKELY(slice_count == sb->capacity)) {
do_embiggen(sb, slice_count, slice_offset);
}
}

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