Re: [Qemu-devel] [RFC PATCH 1/2] ivring: Add a ring-buffer driver on IVShmem

[Borislav Petkov]

On Tue, Jun 05, 2012 at 10:01:17PM +0900, Yoshihiro YUNOMAE wrote:
> This patch adds a ring-buffer driver for IVShmem device, a virtual RAM device 
> in
> QEMU. This driver can be used as a ring-buffer for kernel logging or tracing 
> of
> a guest OS by recording kernel programing or SystemTap.
> 
> This ring-buffer driver is implemented very simple. First 4kB of shared memory
> region is control structure of a ring-buffer. In this region, some values for
> managing the ring-buffer is stored such as bits and mask of whole memory size,
> writing position, threshold value for notification to a reader on a host OS.
> This region is used by the reader to know writing position. Then, "total
> memory size - 4kB" equals to usable memory region for recording data.
> This ring-buffer driver records any data from start to end of the writable
> memory region.
> 
> When writing size exceeds a threshold value, this driver can notify a reader
> to read data by using writel(). As this later patch, reader does not have any
> function for receiving the notification. This notification feature will be 
> used
> near the future.
> 
> As a writer records data in this ring-buffer, spinlock function is used to
> avoid competing by some writers in multi CPU environment. Not to use spinlock,
> lockless ring-buffer like as ftrace and one ring-buffer one CPU will be
> implemented near the future.

Yet another ring buffer?

We already have an ftrace and perf ring buffer, can't you use one of those?

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Boris.

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