| // 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 |