Date: Tue, 21 Nov 2017 15:14:57 -0800 From: John Baldwin <jhb@freebsd.org> To: freebsd-hackers@freebsd.org Subject: Re: hw.pci.realloc_bars Message-ID: <1942153.DdtJSvPgjR@ralph.baldwin.cx> In-Reply-To: <A7DF03C1-C5AE-4A69-ACAB-ADAD3003722A@gid.co.uk> References: <A7DF03C1-C5AE-4A69-ACAB-ADAD3003722A@gid.co.uk>
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On Thursday, October 26, 2017 02:20:23 PM Bob Bishop wrote: > Hi, >=20 > hw.pci.realloc_bars controls a mechanism that repositions a PCI memor= y resource if it can=E2=80=99t be successfully allocated at the default= place. >=20 > It=E2=80=99s disabled by default - anyone know why? >=20 > Seems to me that because it only comes into play in an error case it = would be harmless to have it enabled by default. That would have avoide= d a recent case where installation on the HPE Gen 10 microserver is tri= cky because its VGA suffers from this problem. >=20 > Thoughts? It is disabled by default because it is risky. A correct implementatio= n would first pre-reserve as many firmware/BIOS-assigned ranges as possib= le and only then fallback to allocating resources from scratch. Right now= it tries to realloc as soon as it fails which is before we've reserved firmware-assigned resources of other devices in the system. --=20 John Baldwin
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