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Kernel: Optimize disk reads to read multiple sectors at once 

Old StorageDevice::read_sectors() read each sector separately if the
underlying disk had a disk cache. This patch allows multiple sectors to
be read even if the disk cache exists and contains some of the sectors.

Only sectors that could not be found from the disk cache are actually
read from the disk. This optimization is not done for writing, which
still will write each sector separately, if disk cache has no memory to
store new sectors. It would feel kind of unnecessary optimization as you
have greater problems if disk cache cannot allocate a single page.
This commit is contained in:
Bananymous 2024-05-27 15:52:34 +03:00
parent 8b1514e575
commit a1ab44d39f
1 changed files with 32 additions and 18 deletions
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38
kernel/kernel/Storage/StorageDevice.cpp
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@ -224,20 +224,36 @@ namespace Kernel
{
ASSERT(buffer.size() >= sector_count * sector_size());
{
LockGuard _(m_mutex);
if (!m_disk_cache.has_value())
return read_sectors_impl(lba, sector_count, buffer);
uint64_t sectors_done = 0;
while (sectors_done < sector_count)
{
const uint32_t segment_sector_count = BAN::Math::min<uint32_t>(sector_count - sectors_done, 64);
uint64_t needed_sector_bitmask = (static_cast<uint64_t>(1) << segment_sector_count) - 1;
for (uint32_t i = 0; i < segment_sector_count; i++)
if (m_disk_cache->read_from_cache(lba + sectors_done + i, buffer.slice((sectors_done + i) * sector_size(), sector_size())))
needed_sector_bitmask &= ~(static_cast<uint64_t>(1) << i);
for (uint32_t i = 0; i < segment_sector_count && needed_sector_bitmask; i++)
{
if (!(needed_sector_bitmask & (static_cast<uint64_t>(1) << i)))
continue;
uint32_t len = 1;
while (needed_sector_bitmask & (static_cast<uint64_t>(1) << (i + len)))
len++;
auto segment_buffer = buffer.slice((sectors_done + i) * sector_size(), len * sector_size());
TRY(read_sectors_impl(lba + sectors_done + i, len, segment_buffer));
for (uint32_t j = 0; j < len; j++)
(void)m_disk_cache->write_to_cache(lba + sectors_done + i + j, segment_buffer.slice(j * sector_size(), sector_size()), false);
needed_sector_bitmask &= ~(((static_cast<uint64_t>(1) << len) - 1) << i);
i += len;
}
for (uint64_t offset = 0; offset < sector_count; offset++)
{
LockGuard _(m_mutex);
auto sector_buffer = buffer.slice(offset * sector_size(), sector_size());
if (m_disk_cache->read_from_cache(lba + offset, sector_buffer))
continue;
TRY(read_sectors_impl(lba + offset, 1, sector_buffer));
(void)m_disk_cache->write_to_cache(lba + offset, sector_buffer, false);
sectors_done += segment_sector_count;
}
return {};
@ -247,15 +263,13 @@ namespace Kernel
{
ASSERT(buffer.size() >= sector_count * sector_size());
{
LockGuard _(m_mutex);
if (!m_disk_cache.has_value())
return write_sectors_impl(lba, sector_count, buffer);
}
for (uint8_t offset = 0; offset < sector_count; offset++)
{
LockGuard _(m_mutex);
auto sector_buffer = buffer.slice(offset * sector_size(), sector_size());
if (m_disk_cache->write_to_cache(lba + offset, sector_buffer, true).is_error())
TRY(write_sectors_impl(lba + offset, 1, sector_buffer));