3a96e7373b
Motivation: Add an option (through a SelectStrategy return code) to have the Netty event loop thread to do busy-wait on the epoll. The reason for this change is to avoid the context switch cost that comes when the event loop thread is blocked on the epoll_wait() call. On average, the context switch has a penalty of ~13usec. This benefits both: The latency when reading from a socket Scheduling tasks to be executed on the event loop thread. The tradeoff, when enabling this feature, is that the event loop thread will be using 100% cpu, even when inactive. Modification: Added SelectStrategy option to return BUSY_WAIT Epoll loop will do a epoll_wait() with no timeout Use pause instruction to hint to processor that we're in a busy loop Result: When enabled, minimizes impact of context switch in the critical path
53 lines
1.9 KiB
Java
53 lines
1.9 KiB
Java
/*
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* Copyright 2016 The Netty Project
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*
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* The Netty Project licenses this file to you under the Apache License,
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* version 2.0 (the "License"); you may not use this file except in compliance
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* with the License. You may obtain a copy of the License at:
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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* License for the specific language governing permissions and limitations
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* under the License.
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*/
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package io.netty.channel;
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import io.netty.util.IntSupplier;
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/**
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* Select strategy interface.
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*
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* Provides the ability to control the behavior of the select loop. For example a blocking select
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* operation can be delayed or skipped entirely if there are events to process immediately.
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*/
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public interface SelectStrategy {
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/**
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* Indicates a blocking select should follow.
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*/
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int SELECT = -1;
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/**
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* Indicates the IO loop should be retried, no blocking select to follow directly.
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*/
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int CONTINUE = -2;
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/**
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* Indicates the IO loop to poll for new events without blocking.
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*/
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int BUSY_WAIT = -3;
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/**
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* The {@link SelectStrategy} can be used to steer the outcome of a potential select
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* call.
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*
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* @param selectSupplier The supplier with the result of a select result.
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* @param hasTasks true if tasks are waiting to be processed.
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* @return {@link #SELECT} if the next step should be blocking select {@link #CONTINUE} if
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* the next step should be to not select but rather jump back to the IO loop and try
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* again. Any value >= 0 is treated as an indicator that work needs to be done.
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*/
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int calculateStrategy(IntSupplier selectSupplier, boolean hasTasks) throws Exception;
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}
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