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2005-05-08 10:22:16
Details on the Cache Scrubber
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The cache scrubber reduces the likelihood of EDP, WP, and CP events by shortening the data lifetime in the Ecache, and by eliminating parity errors where possible. (See "Errors and Events" below for an explanation of the EDP, WP, and CP event types.)
The cache scrubber is enabled by default. It scans the entire Ecache of every CPU in the system once every ten seconds.
On an idle CPU, it scrubs all clean lines (lines that are identical to the system memory from where they came), and dirty lines (lines that have newer data than the system memory from where they came) that have good parity. This reduces the lifetime of data in the Ecache on an idle CPU, reducing the likelihood that a parity error will affect critical system or user data.
On a busy CPU, it only scrubs clean lines with bad parity (which might otherwise lead to EDP or CP events). Clean lines with good parity and dirty lines are left in the Ecache so as to not adversely impact system performance.
The cache scrubber never scrubs dirty lines with bad parity to avoid causing WP events. These bad lines could get overwritten by the program using them before they are accessed or flushed, thereby eliminating a bad parity event from occurring at all. (This is sometimes referred to as the natural scrubbing behavior of a busy system.)
Details on the Cache Scrubber
=============================
The cache scrubber reduces the likelihood of EDP, WP, and CP events by shortening the data lifetime in the Ecache, and by eliminating parity errors where possible. (See "Errors and Events" below for an explanation of the EDP, WP, and CP event types.)
The cache scrubber is enabled by default. It scans the entire Ecache of every CPU in the system once every ten seconds.
On an idle CPU, it scrubs all clean lines (lines that are identical to the system memory from where they came), and dirty lines (lines that have newer data than the system memory from where they came) that have good parity. This reduces the lifetime of data in the Ecache on an idle CPU, reducing the likelihood that a parity error will affect critical system or user data.
On a busy CPU, it only scrubs clean lines with bad parity (which might otherwise lead to EDP or CP events). Clean lines with good parity and dirty lines are left in the Ecache so as to not adversely impact system performance.
The cache scrubber never scrubs dirty lines with bad parity to avoid causing WP events. These bad lines could get overwritten by the program using them before they are accessed or flushed, thereby eliminating a bad parity event from occurring at all. (This is sometimes referred to as the natural scrubbing behavior of a busy system.)
Errors and Events
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UltraSPARC processors can detect errors that are reported in the following types of events (as detailed in the UltraSPARC-I/II User's Manual, P/N 802-7220-02):
ETP
A parity error was detected by the CPU when reading from the Ecache Tag SRAM. This is a fatal error because system coherency has been lost. The system will reset (POR) and Starfire domains will arbstop (UPA Fatal error). No Solaris error message will be generated.
EDP
A parity error was detected by the CPU when reading from the Ecache Data SRAM on a cache hit.
LDP
A parity error was detected by the CPU while reading main memory through its Ultra Data Buffer (UDB) chip on an Ecache miss. Note that the Ecache itself is not involved. This can occur when the CPU is reading non-cacheable data (for example, a frame buffer or I/O device), or when filling a line of cache from main memory.
WP
A parity error was detected by one of the UDB chips while data was being written back from the Ecache into main memory. The UDB chips convert the data with bad parity into data with bad ECC, so that a subsequent access to the same physical address will result in a UE. (See UE below.) (The conversion of a parity error to a latent UE does not occur on either UltraSPARC-IIi or -IIe, which is one of the reasons why improved error handling is not available on those processors.)
CP
A parity error was detected during a copyout transaction; that is, a data transfer from one CPU's Ecache to another CPU. This error is detected by the UDB chips of the providing CPU, resulting in the CP event. The providing CPU's UDB chips convert the data with bad parity to data with bad ECC, so that the UDBs of the receiving CPU will report a UE event. (See UE below.)
UE
An uncorrectable memory error has occurred. This event refers to an error in the main system memory, reported by the system data bus on a read access. The underlying source of this error could be main memory, another CPU module (see CP above), or another UPA device (for example, the I/O controller). The UDB chips detect this error.
CE
A correctable error was detected when reading from main memory, or when reading from another CPU's UDB chips. The data read has been corrected and valid data is given to the CPU and the CPU's Ecache. This error is detected by the UDB chips.
BERR
A bus error has occurred during an attempt to read from a memory address. Either there is no device at that address, or the device at that address has returned a bus error. Therefore, bus errors are caused by a programming error or by a corrupted or defective device.
TO
A bus timeout was encountered during an attempt to read from a memory address. Too much time has elapsed waiting for a device at that address to respond.
