chenhengqi / bmc-cache

In-kernel cache based on eBPF.

BMC

BMC (BPF Memory Cache) is an in-kernel cache for memcached. It enables runtime, crash-safe extension of the Linux kernel to process specific memcached requests before the execution of the standard network stack. BMC does not require modification of neither the Linux kernel nor the memcached application. Running memcached with BMC improves throughput by up to 18x compared to the vanilla memcached application.

Requirements

Linux kernel v5.3 or higher is required to run BMC.

Other software dependencies are required to build BMC and Memcached-SR (see Building BMC and Building Memcached-SR).

Build instructions

Building BMC

BMC must be compiled with libbpf and other header files obtained from kernel sources. The project does not include the kernel sources, but the kernel-src-download.sh and kernel-src-prepare.sh scripts automate the download of the kernel sources and prepare them for the compilation of BMC.

These scripts require the following software to be installed:

gpg curl tar xz make gcc flex bison libssl-dev libelf-dev

The project uses llvm and clang version 9 to build BMC, but more recent versions might work as well:

llvm-9 clang-9

Note that libelf-dev is also required to build libbpf and BMC.

With the previous software installed, BMC can be built with the following:

$ ./kernel-src-download.sh
$ ./kernel-src-prepare.sh
$ cd bmc && make

After BMC has been successfully built, kernel sources can be removed by running the kernel-src-remove.sh script from the project root.

Building Memcached-SR

Memcached-SR is based on memcached v1.5.19. Building it requires the following software:

clang-9 (or gcc-9) automake libevent-dev

Either clang-9 or gcc-9 is required in order to compile memcached without linking issues. Depending on your distribution, you might also need to use the -Wno-deprecated-declarations compilation flag.

Memcached-SR can be built with the following:

$ cd memcached-sr 
$ ./autogen.sh
$ CC=clang-9 CFLAGS='-DREUSEPORT_OPT=1 -Wno-deprecated-declarations' ./configure && make

The memcached binary will be located in the memcached-sr directory.

Further instructions

TC egress hook

BMC doesn't attach the tx_filter eBPF program to the egress hook of TC, it needs to be attached manually.

To do so, you first need to make sure that the BPF is mounted, if it isn't you can mount it with the following command:

# mount -t bpf none /sys/fs/bpf/

Once BMC is running and the tx_filter program has been pinned to /sys/fs/bpf/bmc_tx_filter, you can attach it using the tc command line:

# tc qdisc add dev <interface_name> clsact
# tc filter add dev <interface_name> egress bpf object-pinned /sys/fs/bpf/bmc_tx_filter

After you are done using BMC, you can detach the program with these commands:

# tc filter del dev <interface_name> egress
# tc qdisc del dev <interface_name> clsact

And unpin the program with # rm /sys/fs/bpf/bmc_tx_filter

License

Files under the bmc directory are licensed under the GNU Lesser General Public License version 2.1.

Files under the memcached-sr directory are licensed under the BSD-3-Clause BSD license.