--- /dev/null
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+// vim: ts=8 sw=2 smarttab
+
+#include "Readahead.h"
+
+using namespace std;
+
+Readahead::Readahead()
+ : m_trigger_requests(10),
+ m_readahead_min_bytes(0),
+ m_readahead_max_bytes(NO_LIMIT),
+ m_alignments(),
+ m_lock("Readahead::m_lock"),
+ m_nr_consec_read(0),
+ m_consec_read_bytes(0),
+ m_last_pos(0),
+ m_readahead_pos(0),
+ m_readahead_trigger_pos(0),
+ m_readahead_size(0),
+ m_pending(0),
+ m_pending_lock("Readahead::m_pending_lock") {
+}
+
+Readahead::~Readahead() {
+}
+
+Readahead::extent_t Readahead::update(const vector<extent_t>& extents, uint64_t limit) {
+ m_lock.Lock();
+ for (vector<extent_t>::const_iterator p = extents.begin(); p != extents.end(); ++p) {
+ _observe_read(p->first, p->second);
+ }
+ if (m_readahead_pos >= limit|| m_last_pos >= limit) {
+ m_lock.Unlock();
+ return extent_t(0, 0);
+ }
+ pair<uint64_t, uint64_t> extent = _compute_readahead(limit);
+ m_lock.Unlock();
+ return extent;
+}
+
+Readahead::extent_t Readahead::update(uint64_t offset, uint64_t length, uint64_t limit) {
+ m_lock.Lock();
+ _observe_read(offset, length);
+ if (m_readahead_pos >= limit || m_last_pos >= limit) {
+ m_lock.Unlock();
+ return extent_t(0, 0);
+ }
+ extent_t extent = _compute_readahead(limit);
+ m_lock.Unlock();
+ return extent;
+}
+
+void Readahead::_observe_read(uint64_t offset, uint64_t length) {
+ if (offset == m_last_pos) {
+ m_nr_consec_read++;
+ m_consec_read_bytes += length;
+ } else {
+ m_nr_consec_read = 0;
+ m_consec_read_bytes = 0;
+ m_readahead_trigger_pos = 0;
+ m_readahead_size = 0;
+ m_readahead_pos = 0;
+ }
+ m_last_pos = offset + length;
+}
+
+Readahead::extent_t Readahead::_compute_readahead(uint64_t limit) {
+ uint64_t readahead_offset = 0;
+ uint64_t readahead_length = 0;
+ if (m_nr_consec_read >= m_trigger_requests) {
+ // currently reading sequentially
+ if (m_last_pos >= m_readahead_trigger_pos) {
+ // need to read ahead
+ if (m_readahead_size == 0) {
+ // initial readahead trigger
+ m_readahead_size = m_consec_read_bytes;
+ m_readahead_pos = m_last_pos;
+ } else {
+ // continuing readahead trigger
+ m_readahead_size *= 2;
+ if (m_last_pos > m_readahead_pos) {
+ m_readahead_pos = m_last_pos;
+ }
+ }
+ m_readahead_size = MAX(m_readahead_size, m_readahead_min_bytes);
+ m_readahead_size = MIN(m_readahead_size, m_readahead_max_bytes);
+ readahead_offset = m_readahead_pos;
+ readahead_length = m_readahead_size;
+
+ // Snap to the first alignment possible
+ uint64_t readahead_end = readahead_offset + readahead_length;
+ for (vector<uint64_t>::iterator p = m_alignments.begin(); p != m_alignments.end(); ++p) {
+ // Align the readahead, if possible.
+ uint64_t alignment = *p;
+ uint64_t align_prev = readahead_end / alignment * alignment;
+ uint64_t align_next = align_prev + alignment;
+ uint64_t dist_prev = readahead_end - align_prev;
+ uint64_t dist_next = align_next - readahead_end;
+ if (dist_prev < readahead_length / 2 && dist_prev < dist_next) {
+ // we can snap to the previous alignment point by a less than 50% reduction in size
+ assert(align_prev > readahead_offset);
+ readahead_length = align_prev - readahead_offset;
+ break;
+ } else if(dist_next < readahead_length / 2) {
+ // we can snap to the next alignment point by a less than 50% increase in size
+ assert(align_next > readahead_offset);
+ readahead_length = align_next - readahead_offset;
+ break;
+ }
+ // Note that m_readahead_size should remain unadjusted.
+ }
+
+ if (m_readahead_pos + readahead_length > limit) {
+ readahead_length = limit - m_readahead_pos;
+ }
+
+ m_readahead_trigger_pos = m_readahead_pos + readahead_length / 2;
+ m_readahead_pos += readahead_length;
+ }
+ }
+ return extent_t(readahead_offset, readahead_length);
+}
+
+void Readahead::inc_pending(int count) {
+ assert(count > 0);
+ m_pending_lock.Lock();
+ m_pending += count;
+ m_pending_lock.Unlock();
+}
+
+void Readahead::dec_pending(int count) {
+ assert(count > 0);
+ m_pending_lock.Lock();
+ assert(m_pending >= count);
+ m_pending -= count;
+ if (m_pending == 0) {
+ std::list<Context *> pending_waiting(std::move(m_pending_waiting));
+ m_pending_lock.Unlock();
+
+ for (auto ctx : pending_waiting) {
+ ctx->complete(0);
+ }
+ } else {
+ m_pending_lock.Unlock();
+ }
+}
+
+void Readahead::wait_for_pending() {
+ C_SaferCond ctx;
+ wait_for_pending(&ctx);
+ ctx.wait();
+}
+
+void Readahead::wait_for_pending(Context *ctx) {
+ m_pending_lock.Lock();
+ if (m_pending > 0) {
+ m_pending_lock.Unlock();
+ m_pending_waiting.push_back(ctx);
+ return;
+ }
+ m_pending_lock.Unlock();
+
+ ctx->complete(0);
+}
+void Readahead::set_trigger_requests(int trigger_requests) {
+ m_lock.Lock();
+ m_trigger_requests = trigger_requests;
+ m_lock.Unlock();
+}
+
+uint64_t Readahead::get_min_readahead_size(void) {
+ Mutex::Locker lock(m_lock);
+ return m_readahead_min_bytes;
+}
+
+uint64_t Readahead::get_max_readahead_size(void) {
+ Mutex::Locker lock(m_lock);
+ return m_readahead_max_bytes;
+}
+
+void Readahead::set_min_readahead_size(uint64_t min_readahead_size) {
+ m_lock.Lock();
+ m_readahead_min_bytes = min_readahead_size;
+ m_lock.Unlock();
+}
+
+void Readahead::set_max_readahead_size(uint64_t max_readahead_size) {
+ m_lock.Lock();
+ m_readahead_max_bytes = max_readahead_size;
+ m_lock.Unlock();
+}
+
+void Readahead::set_alignments(const vector<uint64_t> &alignments) {
+ m_lock.Lock();
+ m_alignments = alignments;
+ m_lock.Unlock();
+}
Code Review / stor4nfv.git / blobdiff