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Add http2.default_buffer_water_mark config to tune latency #8747

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Merged
randall merged 1 commit into from
May 4, 2022
Merged

Add http2.default_buffer_water_mark config to tune latency #8747

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7 changes: 7 additions & 0 deletions doc/admin-guide/files/records.config.en.rst
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Expand Up @@ -4286,6 +4286,13 @@ HTTP/2 Configuration
frames. Write operation will be triggered at least once every this configured
number of millisecond regardless of pending data size.

.. ts:cv:: CONFIG proxy.config.http2.default_buffer_water_mark INT -1
:reloadable:
:units: bytes

Specifies the high water mark for all HTTP/2 frames on an outoging connection.
Default is -1 to preserve existing water marking behavior.

HTTP/3 Configuration
====================

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4 changes: 2 additions & 2 deletions iocore/net/UnixNetVConnection.cc
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Expand Up @@ -441,7 +441,7 @@ write_to_net_io(NetHandler *nh, UnixNetVConnection *vc, EThread *thread)
int signalled = 0;

// signal write ready to allow user to fill the buffer
if (towrite != ntodo && buf.writer()->write_avail()) {
if (towrite != ntodo && !buf.writer()->high_water()) {
if (write_signal_and_update(VC_EVENT_WRITE_READY, vc) != EVENT_CONT) {
return;
}
Expand Down Expand Up @@ -519,7 +519,7 @@ write_to_net_io(NetHandler *nh, UnixNetVConnection *vc, EThread *thread)
}

int e = 0;
if (!signalled) {
if (!signalled || (s->vio.ntodo() > 0 && !buf.writer()->high_water())) {
e = VC_EVENT_WRITE_READY;
} else if (wbe_event != vc->write_buffer_empty_event) {
// @a signalled means we won't send an event, and the event values differing means we
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2 changes: 2 additions & 0 deletions mgmt/RecordsConfig.cc
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Expand Up @@ -1394,6 +1394,8 @@ static const RecordElement RecordsConfig[] =
,
{RECT_CONFIG, "proxy.config.http2.write_time_threshold", RECD_INT, "100", RECU_DYNAMIC, RR_NULL, RECC_STR, "^[0-9]+$", RECA_NULL}
,
{RECT_CONFIG, "proxy.config.http2.default_buffer_water_mark", RECD_INT, "-1", RECU_DYNAMIC, RR_NULL, RECC_STR, "^[0-9]+$", RECA_NULL}
,

//############
//#
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2 changes: 2 additions & 0 deletions proxy/http2/HTTP2.cc
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Expand Up @@ -812,6 +812,7 @@ uint32_t Http2::header_table_size_limit = 65536;
uint32_t Http2::write_buffer_block_size = 262144;
float Http2::write_size_threshold = 0.5;
uint32_t Http2::write_time_threshold = 100;
uint32_t Http2::buffer_water_mark = 0;

void
Http2::init()
Expand Down Expand Up @@ -843,6 +844,7 @@ Http2::init()
REC_EstablishStaticConfigInt32U(write_buffer_block_size, "proxy.config.http2.write_buffer_block_size");
REC_EstablishStaticConfigFloat(write_size_threshold, "proxy.config.http2.write_size_threshold");
REC_EstablishStaticConfigInt32U(write_time_threshold, "proxy.config.http2.write_time_threshold");
REC_EstablishStaticConfigInt32U(buffer_water_mark, "proxy.config.http2.default_buffer_water_mark");

// If any settings is broken, ATS should not start
ink_release_assert(http2_settings_parameter_is_valid({HTTP2_SETTINGS_MAX_CONCURRENT_STREAMS, max_concurrent_streams_in}));
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1 change: 1 addition & 0 deletions proxy/http2/HTTP2.h
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Expand Up @@ -409,6 +409,7 @@ class Http2
static uint32_t write_buffer_block_size;
static float write_size_threshold;
static uint32_t write_time_threshold;
static uint32_t buffer_water_mark;

static void init();
};
10 changes: 6 additions & 4 deletions proxy/http2/Http2ClientSession.cc
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Expand Up @@ -116,10 +116,12 @@ Http2ClientSession::new_connection(NetVConnection *new_vc, MIOBuffer *iobuf, IOB
this->_read_buffer_reader = reader ? reader : this->read_buffer->alloc_reader();

// This block size is the buffer size that we pass to SSLWriteBuffer
auto buffer_block_size_index = iobuffer_size_to_index(Http2::write_buffer_block_size, MAX_BUFFER_SIZE_INDEX);
this->write_buffer = new_MIOBuffer(buffer_block_size_index);
this->_write_buffer_reader = this->write_buffer->alloc_reader();
this->_write_size_threshold = index_to_buffer_size(buffer_block_size_index) * Http2::write_size_threshold;
auto buffer_block_size_index = iobuffer_size_to_index(Http2::write_buffer_block_size, MAX_BUFFER_SIZE_INDEX);
this->write_buffer = new_MIOBuffer(buffer_block_size_index);
this->write_buffer->water_mark = Http2::buffer_water_mark;

this->_write_buffer_reader = this->write_buffer->alloc_reader();
this->_write_size_threshold = index_to_buffer_size(buffer_block_size_index) * Http2::write_size_threshold;

this->_handle_if_ssl(new_vc);

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6 changes: 6 additions & 0 deletions proxy/http2/Http2CommonSession.cc
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Expand Up @@ -413,6 +413,12 @@ Http2CommonSession::write_avail()
return this->write_buffer->write_avail();
}

bool
Http2CommonSession::is_write_high_water() const
{
return this->write_buffer->high_water();
}

void
Http2CommonSession::write_reenable()
{
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1 change: 1 addition & 0 deletions proxy/http2/Http2CommonSession.h
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Expand Up @@ -103,6 +103,7 @@ class Http2CommonSession
void remember(const SourceLocation &location, int event, int reentrant = NO_REENTRANT);

int64_t write_avail();
bool is_write_high_water() const;

virtual ProxySession *get_proxy_session() = 0;

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12 changes: 6 additions & 6 deletions proxy/http2/Http2ConnectionState.cc
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Expand Up @@ -1655,12 +1655,6 @@ Http2ConnectionState::send_a_data_frame(Http2Stream *stream, size_t &payload_len
return Http2SendDataFrameResult::ERROR;
}

if (this->session->write_avail() == 0) {
Http2StreamDebug(this->session, stream->get_id(), "Not write avail");
this->session->flush();
return Http2SendDataFrameResult::NOT_WRITE_AVAIL;
}

// Select appropriate payload length
if (resp_reader->is_read_avail_more_than(0)) {
// We only need to check for window size when there is a payload
Expand All @@ -1679,6 +1673,12 @@ Http2ConnectionState::send_a_data_frame(Http2Stream *stream, size_t &payload_len
payload_length = 0;
}

if (payload_length > 0 && this->session->is_write_high_water()) {
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@bryancall bryancall Apr 16, 2022

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You are not going to send data to the client unless there is 32k to send?

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@masaori335 masaori335 Apr 17, 2022

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If you're wondering about the timing of the this->session->flush(), it is called with several conditions.

  • e.g. if the response body is 10 bytes, it'll be sent to the client immediately.

This is checking the high watermark of the session buffer to stop it keep growing.

Http2StreamDebug(this->session, stream->get_id(), "Not write avail");
this->session->flush();
return Http2SendDataFrameResult::NOT_WRITE_AVAIL;
}

stream->update_sent_count(payload_length);

// Are we at the end?
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