blob: b431a35239b27b4ce47255fe623cf134d07266bd [file] [log] [blame]
// Copyright 2022 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "quiche/common/quiche_buffer_allocator.h"
#include <algorithm>
#include <cstring>
#include "quiche/common/platform/api/quiche_bug_tracker.h"
#include "quiche/common/platform/api/quiche_logging.h"
#include "quiche/common/platform/api/quiche_prefetch.h"
namespace quiche {
QuicheBuffer QuicheBuffer::CopyFromIovec(QuicheBufferAllocator* allocator,
const struct iovec* iov, int iov_count,
size_t iov_offset,
size_t buffer_length) {
if (buffer_length == 0) {
return {};
}
int iovnum = 0;
while (iovnum < iov_count && iov_offset >= iov[iovnum].iov_len) {
iov_offset -= iov[iovnum].iov_len;
++iovnum;
}
QUICHE_DCHECK_LE(iovnum, iov_count);
if (iovnum >= iov_count) {
QUICHE_BUG(quiche_bug_10839_1)
<< "iov_offset larger than iovec total size.";
return {};
}
QUICHE_DCHECK_LE(iov_offset, iov[iovnum].iov_len);
// Unroll the first iteration that handles iov_offset.
const size_t iov_available = iov[iovnum].iov_len - iov_offset;
size_t copy_len = std::min(buffer_length, iov_available);
// Try to prefetch the next iov if there is at least one more after the
// current. Otherwise, it looks like an irregular access that the hardware
// prefetcher won't speculatively prefetch. Only prefetch one iov because
// generally, the iov_offset is not 0, input iov consists of 2K buffers and
// the output buffer is ~1.4K.
if (copy_len == iov_available && iovnum + 1 < iov_count) {
char* next_base = static_cast<char*>(iov[iovnum + 1].iov_base);
// Prefetch 2 cachelines worth of data to get the prefetcher started; leave
// it to the hardware prefetcher after that.
quiche::QuichePrefetchT0(next_base);
if (iov[iovnum + 1].iov_len >= 64) {
quiche::QuichePrefetchT0(next_base + ABSL_CACHELINE_SIZE);
}
}
QuicheBuffer buffer(allocator, buffer_length);
const char* src = static_cast<char*>(iov[iovnum].iov_base) + iov_offset;
char* dst = buffer.data();
while (true) {
memcpy(dst, src, copy_len);
buffer_length -= copy_len;
dst += copy_len;
if (buffer_length == 0 || ++iovnum >= iov_count) {
break;
}
src = static_cast<char*>(iov[iovnum].iov_base);
copy_len = std::min(buffer_length, iov[iovnum].iov_len);
}
QUICHE_BUG_IF(quiche_bug_10839_2, buffer_length > 0)
<< "iov_offset + buffer_length larger than iovec total size.";
return buffer;
}
} // namespace quiche