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2.主要功能作用
3.MPS控制策略
4.如何更改 1.简介
MPS
该参数含义是一个TLP包里携带的有效净荷的最大值是多少字节#xff08;该限制条件同时适用于写操作和读操作#xff09;。
MRRS
该参数含义是一个TLP读请求包#xff0c;一次最多能向接收端请求读出…
目录 1.简介
2.主要功能作用
3.MPS控制策略
4.如何更改 1.简介
MPS
该参数含义是一个TLP包里携带的有效净荷的最大值是多少字节该限制条件同时适用于写操作和读操作。
MRRS
该参数含义是一个TLP读请求包一次最多能向接收端请求读出多少字节。MRRS参数出现的原因大家有没有想过……其实设定MRRS的原因是为了避免某个设备长时间占用总线 2.主要功能作用
在MPS在PCIe整体性能中有至关重要的作用。随着MPS大小的增加PCIe传输效率也在不断的提升。不过在x86的机器中RC端的MPS通常是128B/256B。在ARM CPU中为了追求高效性能部分场景也会设置为512B。 整个PCIe系统中MPS的大小跟RC、PCIe Switch、Endpoint都有相互的影响最终TLP传输的数据大小取决与MPS最小的一个设备。比如下图示例RC MPS256BPCIe Switch MPS512B但是EP3 MPS128B。所以最终数据传输的大小采用的是MPS128B。
以下是一个实例
lspci -s 01:00.0 -vvvv
01:00.0 Non-Volatile memory controller: Toshiba Corporation Device 0116 (prog-if 02 [NVM Express])Subsystem: Toshiba Corporation Device 0001Control: I/O- Mem BusMaster SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTxStatus: Cap 66MHz- UDF- FastB2B- ParErr- DEVSELfast TAbort- TAbort- MAbort- SERR- PERR- INTx-Latency: 0, Cache Line Size: 64 bytesInterrupt: pin A routed to IRQ 16NUMA node: 0Region 0: Memory at 96200000 (64-bit, non-prefetchable) [size16K]Capabilities: [40] Express (v2) Endpoint, MSI 00DevCap: MaxPayload 256 bytes, PhantFunc 0, Latency L0s unlimited, L1 unlimitedExtTag- AttnBtn- AttnInd- PwrInd- RBE FLReset SlotPowerLimit 25.000WDevCtl: Report errors: Correctable Non-Fatal Fatal UnsupportedRlxdOrd- ExtTag- PhantFunc- AuxPwr- NoSnoop- FLReset-MaxPayload 256 bytes, MaxReadReq 512 bytesDevSta: CorrErr- UncorrErr- FatalErr- UnsuppReq- AuxPwr- TransPend-LnkCap: Port #0, Speed 8GT/s, Width x4, ASPM L1, Exit Latency L0s 2us, L1 32usClockPM- Surprise- LLActRep- BwNot- ASPMOptCompLnkCtl: ASPM L1 Enabled; RCB 64 bytes Disabled- CommClkExtSynch- ClockPM- AutWidDis- BWInt- AutBWInt-LnkSta: Speed 8GT/s, Width x4, TrErr- Train- SlotClk DLActive- BWMgmt- ABWMgmt-DevCap2: Completion Timeout: Range AB, TimeoutDis, LTR, OBFF Not SupportedDevCtl2: Completion Timeout: 50us to 50ms, TimeoutDis-, LTR, OBFF DisabledLnkCtl2: Target Link Speed: 8GT/s, EnterCompliance- SpeedDis-Transmit Margin: Normal Operating Range, EnterModifiedCompliance- ComplianceSOS-Compliance De-emphasis: -6dBLnkSta2: Current De-emphasis Level: -6dB, EqualizationComplete, EqualizationPhase1EqualizationPhase2, EqualizationPhase3, LinkEqualizationRequest-Capabilities: [80] Power Management version 3Flags: PMEClk- DSI- D1- D2- AuxCurrent0mA PME(D0-,D1-,D2-,D3hot-,D3cold-)Status: D0 NoSoftRst PME-Enable- DSel0 DScale0 PME-Capabilities: [90] MSI: Enable- Count1/32 Maskable 64bitAddress: 0000000000000000 Data: 0000Masking: 00000000 Pending: 00000000Capabilities: [b0] MSI-X: Enable Count32 Masked-Vector table: BAR0 offset00002000PBA: BAR0 offset00003000 3.MPS控制策略
pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)tuning and use the BIOS-configured MPS defaults.pcie_bus_safe Set every devices MPS to the largest valuesupported by all devices below the root complex.pcie_bus_perf Set device MPS to the largest allowable MPSbased on its parent bus. Also set MRRS (Max Read Request Size) to the largest supportedvalue (no larger than the MPS that the deviceor bus can support) for best performance.pcie_bus_peer2peer Set every devices MPS to 128B, whichevery device is guaranteed to support. This configuration allows peer-to-peer DMA betweenany pair of devices, possibly at the cost ofreduced performance. This also guaranteesthat hot-added devices will work.
4.如何更改
Linux系统中通过lspci和setpci可以查询和修改MPS/MRRS参数。
比如lspci查看设备DevCap寄存器中MPS512B最终传输用的MPS256BMRRS4KB。
lspci -s 04:00.0 -vvv | grep DevCtl: -C 2
DevCap: MaxPayload 512 bytes, PhantFunc 0, Latency L0s unlimited, L1 unlimited
ExtTag AttnBtn- AttnInd- PwrInd- RBE FLReset
DevCtl: Report errors: Correctable- Non-Fatal Fatal Unsupported-
RlxdOrd ExtTag PhantFunc- AuxPwr- NoSnoop FLReset-
MaxPayload 256 bytes, MaxReadReq 4096 bytes 如果需要修改MPS或者MRRS需要先找到Device Control Register中MPS和MRRS的位置如PCIe Spec定义MPS在bit5-7MRRS在bit12-14. 同时Device Control Register的offset是0x8h。
